This happened to me until I added {absolute_codec_string='PCMU,PCMA'} on the dial string.

From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of Michael Collins
Sent: Friday, February 04, 2011 11:13 AM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Grandstream Freeze on Originate command

Do you have an example of an invite to the GS, perhaps from Asterisk or another SIP server, that does not freeze the phone? My guess is that GS is doing something silly. (They're known for doing silly things and freezing up when you send them an invite is, unfortunately, not at all surprising given the reputation they've acquired for themselves.)

Wish I could help more...

-MC