Connecting from WM5

I am using Asterisk on a CentOS 5 system. The PC is on my internal LAN. No outside access of any kind.

I can connect to it using XLite for Windows, dial, receive, etc.

However, I am getting errors when using XLite on an iMate JasJar which run WM5.

I turn on the Wifi of the cellphone and connect to my LAN. I start up XLite and give the credentials:
Display name: test
User Name: 104
Password: 104
Domain: asterisk
SIP Proxy:

BTW, the above credentials work fine on XLite for regular Windows.

Xlite on my cellphone logs in successfully. If I try to call another extension, I get an error on XLite saying: Error 499 Request Pending

The Asterisk CLI gives two messages:

    -- Registered SIP '104' at port 5060
  == Using SIP RTP CoS mark 5

[Mar 16 13:16:14] WARNING[12831]: chan_sip.c:2794 retrans_pkt: Maximum retries exceeded on transmission 444414AD-A101-9D22-8BBF-F372447E99BF@ for seqno 3551 (Critical Response) -- See doc/sip-retransmit.txt.

Any ideas as to what causes this? I’m not very familiar with Asterisk (read: nearly ignorant)