Is it possible to fake the caller ID on a landline phone? I have learned to be very wary of those who phone unexpectedly and conceal their ID as ‘Private number’ but I have recently got some calls that are very suspicious that seem to have odd numbers. One showed the caller and the number as “2004” which isn’t likely to be a valid phone number in many places. Others showed long numbers that could have been valid here but the caller was a recording or a scammer.
So technophiles can it be done?
I don’t answer any “private number” calls at all these days, as most of them have turned out to be scammers or someone trying to sell me something I have no interest in. If they are a genuine caller, they can leave a message or SMS me.
Edited to add: yes it can be ‘faked’ …
I’m with Gordon. My mobile is set to push any call that isn’t in my address book straight to voice-to-text message service without even ringing - even if they present a number, if I don’t know it, they can talk to the computer first. That might be inconvenient for some, but I don’t use a mobile at work (prohibited at the site) and we have bad coverage anyway - after hours there’s probably only a handful of people crazy enough to ring me anyway. My home service gets a lot of bogus calls, being it is a VoIP service with a direct in-dial number in each capital city and one locally here, so I get a lot of calls from people who think they’ve called ‘Dave in Norwood’ and seem perplexed that a number they thought was in Adelaide is ringing in the outback 
To address that I’ve played a little with a Raspberry Pi 3 and some funky software that can do all sorts before letting the caller through to an actual phone.
Don’t trust that you can always block caller-id either. I received a number of prank calls from a blocked number a few years back - when I approached my VoIP provider with the complaint they actually told me the callers number, a person who was then ‘just somebody I used to know’, to borrow a line. I was more than a little surprised they divulged the information but with it I was able to stem the flow of calls
Yes, it can be done, and has been done. The increasing prevalence of VOIP (Voice Over Internet Protocol) makes caller ID spoofing (faking) easier to achieve.
Following on from @ScottOKeefe…
Here is a link to more information on caller id spoofing.
And an article in Business Insider which also talks about spoofing.
We have an answering machine and I don’t pick up any phone number I don’t recognise…let the answering machine answer the call. Should it be a scammer with a spoofed caller id they will hang up. If it happens to be a friends or others they often start to leave a message and we can pick up the call and interrupt the message being left.
We also check the caller’s number by doing an online search (google the number shown) to ensure that it wasn’t someone we know (friend or business) just in case they decided not to leave a message. Online searching also allows one to see if there are any complaints from others about the caller id number.
We do likewise for private numbers.
If using Skype or similar VOIP services you can pay to get a number or numbers from various parts of the world and use which one you want at any time.
I have included some info from Skype on the numbers/countries available through them and as you will see Australia is available through all types of accounts without restriction, some countries do restrict this facility to only residents of their country though if a registered company in that country they can also register :
"How do I set up a Skype Number for another country?
You can buy a Skype Number for most countries they’re available in, even if you don’t live there. Find out which countries Skype Numbers are available in.
However, some countries require proof of residence, so unless you have a valid address there, you won’t be able to get a number for that country. These countries include:
Brazil
France
Germany
The Netherlands
Switzerland
South Korea (Skype Numbers in South Korea must be purchased through our partner, Daesung.)
Verification of your registered address may vary across individual countries. The following example is for purchasing a Skype Number in Germany:
Sign in to your account.
In the Manage features section, select Skype Number, then select Get a Skype Number and follow the instructions.
In the ‘Information required for a Skype Number subscription’ page that opens, enter your valid registered address in Germany and your email details. Then check the box to confirm that you’re a resident of Germany and to accept passing your details to a German service provider.
Select Next, choose whether you want a 3-month or a 12-month Skype Number subscription, then complete the payment.
Your details will be shared and verified by the service provider and you’ll receive an email to let you know when your Skype Number has been activated."
"Skype Numbers are available to purchase in many countries and on any Skype account. Check one of the lists below for available countries by account type.
Available countries for personal accounts
Australia
Brazil*
Chile
Denmark
Estonia
Finland
France
Germany*
Hong Kong
Hungary
Ireland
Japan*
Malta
Mexico
Netherlands
New Zealand
Poland
Romania
South Africa
South Korea
Sweden
Switzerland*
United Kingdom
United States
*Unavailable for purchase with Skype Credit.
Available countries for Skype Manager accounts
Skype Numbers available for purchase through a Skype Manager account that is not registered in the United States:
Australia
Chile
Denmark
Estonia
Finland
France
Germany
Hong Kong
Hungary
Ireland
Japan
Malta
Mexico
Netherlands
New Zealand
Poland
Romania
South Africa
South Korea
Sweden
Switzerland
United Kingdom
Skype Numbers available for purchase through a Skype Manager account registered in the United States:
Australia
Chile
Denmark
Estonia
Finland
Hong Kong
Hungary
Malta
Mexico
Romania
Sweden
United Kingdom
United States
If you purchased a Skype Number through Skype Manager before September 2, 2010, from a country not listed above, you will still be able to use that Skype Number, and renew it if you want."
Skype Caller-ID is a user definable field in the Skype phone profile… It can be hit or miss in the US, and I assume it is the same around the world where most times Skype will display the user-defined Caller-ID number, but not always. When it does not display the defined Caller-ID, it will display the number of the Skype node that physically made the call.
A reason for them supporting a user-specified caller-ID is that you usually want to be identifiable to the person you call, so it is generally set to your real phone number. Obviously that VOIP service feature is open to abuse, but.
If you have a number you don’t know come up, you can look it up an a reverse phone website such as http://www.reverseaustralia.com/ You will usually find that other people have left comments about a particular number, so you can find out whether it is legitimate.
We have found recently that scammers are starting to poach real numbers when using caller id spoofing. There has been several in the past month which are residential properties and no comments being left as assume the number is only spoofed for a short time. I expect the landline number owner is unaware that their number has been spoofed by scammers.
It appears the scammers are trying to get around such checking by call receivers.
If I don’t know the number, I don’t answer but let my answering machine answer the call. Scammers usually hang up…unless they are the odd brazen one that does.
The Skype number that I referred to above is an actual listed number in the telephone number registry as if you really do reside in the listed country. So not just an easy to abuse system but a custom made one for scammers unless you’re in one of the countries that requires a “real presence” to use it. Australia could easily require the same policy to list as those few countries such as Germany do already.
That is indeed the case. I have a US presence and family there. I have many “international mates” who also find Skype numbers to be a glue that helps keep things together.
That being written, everything you wrote about it enabling and abetting scammers is right on, but everyone who is doing the right thing is increasingly marginalised by those who do not.
I don’t have caller ID but I have recently been getting calls from “Telstra” (we don’t use Telstra). I normally hang up but this week I asked the caller, Jack Wilson, if I could call him back. He gave me a Melbourne number and asked when would I call back - I said I didn’t know and hung up. I of course haven’t rung back. The next day I received a call from Jack at “Microsoft” - same guy? - possibly. I just hung up. I’ve had dozens of these calls over many years 
YES
For landline calls, as you have Caller ID unless the Caller ID is in the correct format for an Australian or international number or if it’s “hidden” you can allow it to go to voicemail
If you have Caller ID software you can have:
If you have an Android smartphone the “free” app Mr Number has a very comprehensive database of scammers and can automatically dump them without even ringing
It can also send "faked’ or hidden Caller ID to voicemail or dump them without even ringing
It’s very customisable.
Real techo’s with a mean steak can investigate “It’s Lenny”
Just a small note about some calls that come up as private number or caller ID unavailable.
I work in clinical trials, and our study nurses experience considerable difficulty contacting some patients, as they do not answer calls. Hospital and university pabx and other phone systems do not necessarily supply the caller id info, so we come up as Unknown or Private number. Even putting our number into your saved numbers will not solve this issue. Of course, we will leave a message, but only if you give us the capability. What I mean is, sometimes we can’t successfully leave a message. Some people default to no voice mail, some to a generic message that present problems for us being sure we have reached the correct person, and some mobiles have the dreaded "leave a 10 second message’ that will be converted to text. I often get garbled text conversions, not sure about anyone else. And, if we are calling from work, we can’t text you as we do not have that capability. We are on a landline. So the “I don’t answer any “private number” calls at all these days” is problematic for us, and getting more so, as many people decline to give us an alternate number “cos you can always get me on my mobile”.
Similar situation as above comments. My Dad has a Private “Blocked” number due to us being Asian and getting some abusive phone calls. When he calls I won’t know it’s him. Being aged I need to take the call in case he is in trouble. Can’t have it both ways!!
I just got one a few minutes ago - tried to call the number back, but it wasn’t a legit number. I get two or three “Telstra” calls a day!
My own number blocks my ID … but I may drop that as it seems to make no difference and just irritates my family. 8*)
You need to be aware that you might be ignoring an important call. For example, calls made from public hospitals often show as a Private Number.
Honest callers will leave a message. The danger is the message is garbled and unintelligible for one reason or another, be it digital distortion or the person on the other end not speaking clearly and slowly enough.
As TheBBG says, they can leave a message if genuine. Even if it is a bit garbled, I’d probably phone back. However, saying I might miss an important call from a hospital is a bit of a long shot, given that in 15 years of mobile phone ownership, I’ve never had such a call.
For hospital employees, it is a common problem!
