Have a digium TDM400P card which is converting 4 analog lines into the asterisk server. When you call in from another phone line, and try to dial an extension, it doesn't seem to recognize the inputted numbers while the "welcome" message is playing. If you wait until the welcome message has stopped playing, and enter the extension in it works. I believe this is the DTMF?
I have seen this issue with SIP providers before, but not with analog lines.