I have used a Nokia Lumia 710, but it was horrible. A lot of signal drops, and the signal itself wasn't stable. Also, the signal bar reaches 3/5 maximum at home, and the funny part is that Calls don't connect at signal 2/5 ! Even if calls were connected, A LOT of voice cuts and echoes and the other party couldn't understand 50% of what I am talking, due to voice cuts and muffing voices. So it was a mess.
Now, I took my father's Samsung Galaxy Fit, which at least does 4/4 and 3/4 indoors, and signal doesn't drop nor calls drop. Even in my room, which is nearly a dead spot on 3G network, the Galaxy Fit "resists" the dead spot and gives me 2-3/4, while my previous Lumia 710 gives up immediately, giving me a 1/5 maximum.
But this phone is kinda old and laggy. Also, I am not a fan of Samsung devices, due to the cheap body materials and the crowded TouchWiz UI.
So, Any advices for the smartphone with the best signal and the best in-call voice quality for both ends ? Preferable Sony, HTC, and WP devices. And No Samsung.