Iphone 3G-> weak/no service on 4.2.1|unable to install 4.1|no bars on 3.1.2

[Adamov]

Hello. I have a strange problem with my iPhone 3G 8Gb, and i hope that You can help me to fix it.

Facts about iPhone
*factory unlocked
*baseband 05.15.04
*water damaged->no
*dropped-> no
*gps, wifi, bluetooth->ok
*shsh files-> 4.1 4.2.1

Before problem:
Iphone has 4.2.1 works quite fine(full bars, yes) but there were small problems during phone call; sometimes i was getting 'call failed' then 1bar for a second and after that i couldn't make a call(silence in speaker). I thought that it was a problem with carrier not with iphone.... Yesterday during call iphone shows 'end call' and that was end for real

Problem:
#When Iphone has firmware 4.2.1 there was 1-2 bars/no service of 3g(should be 4-5); and no service/searching.../unable to load carrier list, if i switch on 2g.
I switched airplane mode on/off,reset networking settings, and made a lot of restore too.
#If i want to install 4.1(shsh files present), progress bar in itunes grow to 2,5cm and stops; nothing happens for hours and i don't get any errors.
I tried to install custom firmware, but then itunes showed me errors: 1600 1601. iReb didn't helped
#I can install 3.1.2, but then i have no bars, and nothing helps.


If You know what to do with this issue, please let me know. I will be grateful.
PS: Sorry for my pathetic english...