Jail broken AT&T iphone 4 for T-Mobile. Why can't people hear me?

I bought the jail broken iphone 4 back in May and before it used to make phone calls just fine. After a couple months people can't hear me, but I can hear them. I can make phone calls and people can call me, but I don't know what the problem is. There's no water damage or anything. What should I do?

Btw, I have good service all the time, so it doesn't make any sense.

If you have good service then phone is probably broken.

Try to use an original iphone earphone if it works.