My First iPhone Trouble. Tips for a replacment?

[TheCheapGeek]

Ok i have had the 3g since launch day and the original iPhone since last September. This is the first time that i have considered taking my phone into apple in attempts to get a replacement. There are several places it happens, but my phone will rapidly drop from full 3g to a "no signal" message and stay there untill I either switch off my phone or toggle airplane mode. This is all while next to another 3g where the signal doesn't budge. I can't be without my phone so on my next trip through Houston i am going to drop by the Apple store and try and get a replacement. Is this a hardware issue warranting of a new unit? What can i do to ensure that i can get a replacement and not a repair? Also i have restored the phone many times, including DFU mode restores. I also never restore from a backup, it humors me that i jail broke and unlocked my 1st gen repeaditly and never had any issues and when i go legit, there are issues. Any other tips?