Please help troubleshoot unlocked Samsung E250...

Question

I recently purchased a Samsung E250 from Ebay...the phone is unlocked and supports my network(AT&T) just fine...my problem is when I go to make a phone call it shows the "call in progress" on the screen but it never connects and I cannot hear it ringing...also, if someone tries to call me it goes straight to my voicemail even though my phone is turned on with good signal strength. Is there something wrong with the handset or is it a setting I am missing??Please help...thank you!!~ASH~