Iphone 4 i can hear them but they can not hear me , help ?

[YANNISS2009]

i bought unlocked iphone 4 . 4.0.1 version . when i make a call they can not hear me but i can . only few times happen they hear couple words and then it's gone . i updated to 4.1 keeping the baseband so when i use my t-mobile card again same problem . we tried many card same thing .
took it to a repair guy. he said he does not think is the micro becuz he can record using voice recorder. im lost where i can go to figure it out . anyone has any idea???/ plz your help is appreciated .

 

[Pocobear]

Just a thought, have you tried it on speaker phone? Have you tried a soft=reset? Hold the Sleep and Home buttons down at the same time for about 10 sec, until the apple icon appears on screen, then release and wait for it to reboot.