always full service but not possible

my phone always shows full service and i know this is not possible where i live. the other night i was in the internals and went to test mode and clicked on "RF test" then "gsm test" and i clicked on "set egsm-mode". my phone rebooted and i had no service, completely none at all. i freaked out turned my phone off and had plans on calling att in the morning to say my phone wasn't picking up service signals. in the morning i turned it on and it took a while to turn on for some reason and once it did i got an insane amount of messages from about 9ish when i clicked on the "set egsm-mode". now my phone shows that i have full service all the time and i tried to go back in the gsm test to click on reset like u can with utms test if u click on set mode u can go back and click reset. now my phone shows i always have full service, which is nice but i think it is wrong because it can be beside another att phone that has none. places in my house where are dead zones show full service on my phone but i cant send messages or access the internet. should i call att to get a replacement or just let this go? i got the phone june 1st of last year so i dont have much time till my one year is up, altho i do have the insurance. so i would like to know what i should do with this problem