I just started having the same issue as outlined above on my 3 year old HTC Incredible, cannot make phone calls or texts, but internet works fine. The error message is SMS error Cause Code: 32773, error class 3.
Called my cell from land line and get message that cell phone number is not available.
One other thing happened, Yahoo mail service switched to secure SSL, i.e. went from http to https last night. The mail works fine. I am not sure if this is connected to the problem I am having or why it would affect phone calls?
Are there any solutions beyond the standard 'buy a new phone'?