Try this hypothesis out for size to account for dropped calls: Your iPhone is not the only phone using the network at any given time (to state the obvious), therefore when you initially initiate a call you may display relatively decent signal strength (accurately or not given Apple's recent statement). However, as newer calls are initiated and accepted on to the cell tower, this congestion/bottleneck causes your 'established' call to be virtually pushed off the network to accommodate the newer call. This may also be further exacerbated by the antennae attenuation phenomenon. It may be also worth considering the type of SIM that is being used too, in that those with a contract SIM may have priority on the network over and above those with a PAYG SIM in this situation. Thoughts.......?