asterisk users - Nov 2009 - Got SIP response 420 "Bad Extension" back from inphonex.com

Hello:

New to asterisk and hoping to use for http://summitcamp.org research 
station.

While trying to use with Inphonex I find that incoming calls drop after 
about one minute--
     -- Got SIP response 420 "Bad Extension" back from 208.239.76.169
   == Spawn extension (incoming-inphonex, 210, 1) exited non-zero on 
'SIP/inphonex-095bf208'

Found that I can use `*CLI> sip set debug peer inphonex` to see more 
information, such as--
<--- SIP read from UDP://208.239.76.169:5060 --->
SIP/2.0 420 Bad Extension
Via: SIP/2.0/UDP 
64.165.113.66:5060;received=64.165.113.66;branch=z9hG4bK121e8b66;rport=5060
From: 
<sip:s-3sdr5c32d1q71 at
10.0.5.66:5060;useradd=64.165.113.66;userport=5060;transport=udp>;tag=as111b0d1e
To: Unknown <sip:6508592000 at 67.16.112.165>;tag=SDbapb901-2318a5d8
Call-ID: SDbapb901-ff4e360f8a8714144f03eb06aad237b5-gurpkk2
CSeq: 102 INVITE
Unsupported: timer
Content-Length: 0

The best I can figure is that inphonex does not support session-timers 
because when I insert the following--
sip.conf
--------
|session-timers=refuse

The calls do not drop.  Question is simply whether this will haunt me 
elsewhere.

Thanks,
Andrew


Using CentOS release 5.4 (Final) / asterisk16-1.6.0.17-1_centos5

Registered to Inphonex--
register => virtuser:passwd:virtuser at sip.inphonex.com:5060/DID
[inphonex]
username=xxx
type=peer
secret=xxx ; password used to login their website (same as in register =>)
host=sip.inphonex.com
fromuser=xxx
fromdomain=sip.inphonex.com
context=incoming-inphonex ; context to be used in extensions.conf for 
inbound calls from inphonex
canreinvite=no
insecure=invite