I'm no expert, but the radio/modem is basically the phone part of your phone - the communication part. There's a new version (is it firmware? I guess so) to flash which for some (like me) has improved reception. I don't think I've seen it do anything BAD, but I could be wrong. I got it from the Beans Rom thread. As always be careful, CHECK THE MD5, and I'm not sure if it needs a specific os version, but I installed it when I upgraded to Beans build 9.
It is in the second post here http://forum.xda-developers.com/show....php?t=2032447
(beans thread) or I'm sure you could search the forums for "VRALL4 Modem"