Cisco - almost there?

I am attempting to connect to Cisco 12SP phones. I have dial tone on both, but if I press any numbers I get a fast busy signal. From a working SIP phone, if I dial the extension for either of the Ciscos, I get “the person at xxx is on the phone”.

Any ideas?

What is your configuration, dialplan and output from a verbose CLI? Without these details, it is difficult to say what the problem may be.