[fi0660]

Carries can save money by having less towers but by using higher transmit power. I have heard that this can show up as the phone reporting full bars, but not being able to initiate/receive calls due to insufficient transmit power in the phone.

[pyre]

While possible, that doesn't seem likely. Doesn't the phone have to do some sort of handshake with the tower to even show the bars? Or are you saying that the phone only has enough power to do the handshake?

[fi0660]

My understanding is that when the phone is idle, bars are commonly measured based only on the quality and strength of the incoming signal. The outgoing signal might be stable enough for a handshake but not for a call.

Of course the other possible explanation for full bars but no calls is that the network is busy.