i don' know if this is caused by apps and tweaks that i did. i always set my phone on 2g for battery conservation. lately, even with a couple of restart and switching bands to 3g and dual and then back to 2g, i don't get a 2g signal. i tried to call for it to search for a reception but it says no reception. i need to repeat restart and band switching a couple of times in order for the 2g antenna to work. 3g seems fine though...
Well, I might have a related problem myself: My phone sometimes just decides not to be online and I have to manually switch to 3g back to 2g to get a connection, and somehow my phone stopped using umts and only uses hdspa to transfer data. It's not that it doesn't connect on 3g, it simply doesn't do anything.