[asterisk-users] DTMF not working using *98, but OK on inbound routes?

[Doug]

Has anyone seen anything like this:

I dial *98.  Asterisk says "Password?"   I punch in
the password, and the system doesn't recognize the
tones.

However, if I dial my own number and ignore the
incoming call, it goes to voicemail, and then
I can get into voicemail.

I have a sneaking suspicion that Asterisk is
somehow not recognizing the DTMF tones somewhere
along the way.

This happens intermittently with Linksys ATAs and
Polycom phones.  Using a Cisco 3640 VOIP router.

Any ideas on what to check?