Landline cables for Optus NBN

Is there any difference in my old cable for my landline phone and the new grey and short cable for the new Optus modem? Optus told me to buy an RJ45 model as their cable is too short.
Their new modem has cut outgoing and incoming calls.


If you are referring to the cable that plugs into your wall socket that delivered the connection to your landline phone and your ADSL modem, there is no difference except that you need to remove the ADSL splitter if you had one.

The cable from the wall socket then connects directly to the NBN router, and depending on the router and your service, you may be able to still connect an existing analogue handset to the router, but your old landline handset cannot directly connect to the telephone exchange as there is no copper pair all the way back there.

If it cannot be connected successfully connected to the NBN router, you will need to replace it with a VOIP handset providing your NBN modem and NBN service provides that facility.

If the cable supplied is not long enough, Jaycar and many other electronics retailers can supply longer cables at budget prices.

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The cable is no different, but the difference between the old tried and true PSTN (copper phone service) and NBN’s VOIP is dramatic. VOIP is all digital and depending on your modem and RSP there are many anecdotal stories about ‘bad quality’ to be polite.

To your problem and assuming there is not more to your problem, sometimes one can get a cable with a dodgy plug; your best first try should be to carefully re-seat the cable in the modem/router VOIP socket and your phone. If that does not resolve it try another cable. If you can use the ‘too short’ one and it is fine, you have a dodgy long cable; replace it with a different brand to assure a different plug.

Although the venerable RJ45 plug is standard I have encountered products that seat very well, as well as not well at all.

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Thank you TheBBG.
Together with Fred’s explanation, I think it is the old cable!
I will let you all know whether the new RJ45 works or not.



Firstly, did you order a connection with VOIP (Voice over IP) that provides your phone line? If not, you won’t make/get any phone calls. via your modem.

Secondly, if you ordered VOIP, is the modem VOIP equipped? That is does it have modular phone ports (the green section in the image below) along side the data ports? If not, you won’t make/get phone calls.

If your old landline phone had a four pin modular plug, it was a RJ11 plug (image below). Your RJ11 phone cable connects into the phone port in the modem. NOT between the wall and the modem.

If it is an RJ11, this is the most likely cause of your modem not behaving.

To connect to your modem to the wall socket you need an RJ45 (image below) which has eight connector pins.

If this was not provided by Optus, I would be asking Optus to provide one ASAP, (and they shouldn’t bill you for the NBN until you receive it).

Until that arrives; in case you don’t have a spare suitable RJ45 cable, they can be purchased from the cheap stores, from K Mart, Big W etc, Officeworks, any computer store, Bunnings, or as @Fred123 correctly pointed out, from Jaycar.

Please note that price does not correlate with quality so you don’t need to pay a fortune. I have picked up quite a few unopened packets of cables from op shops for only a couple of dollars each.

If you are buying a cable, look for the “Cat” (Category) number. Cat 4 is the minimum you should buy. The bigger the number the faster the cable. Cat 5e is faster than Cat 5. Cat 6 is faster than Cat 5e. Cat 6e is the current fastest. The faster the cable, the more it will cost. Without knowing your data plan speed, generally it is better to get a faster cable to handle higher through-puts.

If you already have a RJ45 cable installed, you need another one to see if the cable you have is at fault for the loss of phone line.


Hi meltam
I had to purchase an RJ12 cable (10 metres) from Office Works.
That was the key.
In the end, an Optus Technician arrived a few days ago. He found
issue was their end (which was always the case). Now fixed and together with the new RJ12 cable, I expect no further problems.
Optus should have supplied a variety of lengths for their cable. They are always reluctant to send their Technician, advising the customer to ask a friend to assist. Fobb-off!!


I bought an RJ12 from Office Works. Optus Technician arrived a few days ago. The issue was always with their end. Now telephone works. I expect no further problems. Optus always fobb-off their customers by telling them to find a friend to assist. So much for service. If I had a Facebook account, I am sure the landline would have been fixed weeks ago! I am a skeptic about modern media platforms. Have not joined My Health Record either.