Help HELP PLEASE: I bought a used G2X and can't hear anyone unless I use earphone or click Speaker button

[magentawave]

I just bought a used T-Mobile G2X and I can't hear anyone during a phone call unless I use my earphones or click the "Speaker" button but apparently they can hear me. And yes, I do have my phones volume up. This phone is NOT rooted. Does anyone know how I can fix this problem?

Thank you very much.

Steve

P.S. Aaargh, I hope I didn't get ripped off from buying this phone.