I'm very happy with 3CX on my Hero phone, apart from a couple of issues:
1. I use a dialer called Eir Fast Dialer, although the problem also manifests when dialing by clicking on a phone number in a Text message. 3CX kicks in automatically and dials the required number, which is exactly what you'd expect. However, when I hang up, the phone goes into a reset cycle, as though I rebooted the Android system. This doesn't happen when I dial directly from 3CX. Very annoying.
2. The call log integration doesn't work. It either enters unknown numbers in the call log or doesn't enter anything.
These two issues together force me to use a lengthy and cumbersome method of dialing. Each time I dial or redial, I go into my contacts from 3CX (good integration with Google contacts), find the number and dial. Since there is no usable call log, I have to repeat this procedure each time I redial a busy line.
Two nice features that would probably be easy to put into 3CX would be its own Speed Dial (dial a preset number by a long press on a digit), and its own call log or at least a last number redial.
If, however, the two above issues can be fixed then the Android dialer's functionality would work seamlessly with 3CX, making the above requested features redundant.
I tried other popular SIP clients. They also have problematic issues (maybe it's my phone doing it) but so far have yet to find a client with such clear audio and such good integration with Google contacts. Please fix the above, to make 3CX a real winner overall.