asterisk users - Jun 2004 - SNOM 200 using GSM Codec dtmf problem

Hello All, 
I'm trying to get my SNOM 200 to work using the GSM codec. The problem is it
wont' pass dtmf digits. I have it dtmf outband on, inband off. In my
sip.conf I have dtmfmode=rfc2833. Whenever I press a digit on the snom phone I
get "invalid gsm data" so I think it's a configuration problem in
the snom, anyone have a working configuration using gsm?
Thanks
-Matt
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