Audiovox 5600 Calling trouble

[Guest Coolcom]

I have an Audiovox 5600 on the USA Cingula* network. Quite often, i will be in the middle of a call and all of a sudden i can't hear the other person, it just cuts out, but they can hear me perfectly, then, suddendly, sometimes after 2 minutes, they will come back to say that they heard everything i said but i couldnt hear them! Recently, its been happening before i even get on the line, i make a call but i can't hear the phone ring, they pick up, i dont hear them, then all of a sudden they come "back" and i can hear them. I called Cingula* and they claimed it is a SIM card issue (my SIM card is almost 3 years old) do you think this is the case? I konw may other people on the same network with different phones that are having the SAME issue, verbatium. My SMT 5600 is about 4 months old, i bought it brand new.

Thanks for your help!