I am less than 1km from the local tower (Telstra, Optus, Vodaphone). My house is "over the crest of a hill" from the tower and I have that problem on the Optus network in half my house that varies from 0 to 2 bars while the other half fluctuates between 2 to 5 bars. The partner has a Telstra data SIM in her 3G iPad and it is similar. Back in the USA I frequented a private airport in suburban Houston TX, and the mobile coverage around the hangars was similarly unreliable. While on a recent trip to SA I was surprised at how often we went to no service for 10+ minutes at a time along the main roads.
All the while the companies are resisting having to open their services for roaming to ostensibly protect their interests; in these times of no phone booths, increased travel and thus breakdowns outside metro areas, and the need to just communicate, the interests of all of us have been and continue to be held subservient to businesses' profits. The telcos could, as was once the case in the USA, simply charge "bigly" for roaming minutes, but that would be too easy a solution to address their profit motive, I guess.