When executed on interop.pingtel.com, the following dialogwatch obtains no event information:

 $ /usr/bin/dialogwatch sip:1562@interop.pingtel.com dialog
resourceId 'sip:1562@interop.pingtel.com' fromUri 'dialogwatch@interop.pingtel.com' toUri 'sip:1562@interop.pingtel.com' event 'dialog' content-type 'application/dialog-info+xml,multipart/related,application/rlmi+xml,application/reginfo+xml' port=0 expiration=300
Subscription attempt succeeded. Handle: 's-62687322b874c920-1,33b86f49,'
subscriptionStateCallback is called with responseCode = 200 (OK)
[no event body forthcoming]

It appears that the problem regards the Contact header that the SipUserAgent applies to the outgoing SUBSCRIBE. The SUBSCRIBE is:

SUBSCRIBE sip:1562@interop.pingtel.com SIP/2.0
From: <sip:dialogwatch@interop.pingtel.com>;tag=c211f5c0
To: sip:1562@interop.pingtel.com
Call-Id: s-e0e1af501b834ad0-1
Cseq: 1 SUBSCRIBE
Event: reg
Accept: application/dialog-info+xml,multipart/related,application/rlmi+xml,application/reginfo+xml
Expires: 300
Date: Thu, 07 Feb 2008 19:49:29 GMT
Contact: <sip:155.212.198.118:36801;transport=udp>
Max-Forwards: 20
User-Agent: sipX/3.9.7 (Linux)
Accept-Language: en
Supported: eventlist
Via: SIP/2.0/UDP 155.212.198.118:36801;branch=z9hG4bK-sipX-000185436c5d73a453b131025572c03a9d3b
Content-Length: 0

But the address/port in the Contact header is not opened. The open ports are:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 155.212.198.118:36681 0.0.0.0:* LISTEN 3221/dialogwatch
tcp 0 0 192.168.122.1:36681 0.0.0.0:* LISTEN 3221/dialogwatch
udp 0 0 192.168.122.1:36801 0.0.0.0:* 3221/dialogwatch
udp 0 0 155.212.198.118:36802 0.0.0.0:* 3221/dialogwatch
udp 0 0 192.168.122.1:36806 155.212.198.118:5060 ESTABLISHED 3221/dialogwatch

This seems to have something to do with the multiple interfaces on the host:

$ /sbin/ifconfig

eth0 Link encap:Ethernet HWaddr 00:E0:81:04:F5:10
          inet addr:155.212.198.118 Bcast:155.212.198.127 Mask:255.255.255.192
          inet6 addr: fe80::2e0:81ff:fe04:f510/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:504382 errors:0 dropped:0 overruns:0 frame:0
          TX packets:390966 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:364483391 (347.5 MiB) TX bytes:106566736 (101.6 MiB)

lo Link encap:Local Loopback
          inet addr:127.0.0.1 Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING MTU:16436 Metric:1
          RX packets:507961 errors:0 dropped:0 overruns:0 frame:0
          TX packets:507961 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:263028390 (250.8 MiB) TX bytes:263028390 (250.8 MiB)

peth0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
          inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
          UP BROADCAST RUNNING NOARP MTU:1500 Metric:1
          RX packets:638697 errors:0 dropped:0 overruns:0 frame:0
          TX packets:391715 errors:0 dropped:0 overruns:0 carrier:0
          collisions:92992 txqueuelen:1000
          RX bytes:374345133 (357.0 MiB) TX bytes:106639131 (101.6 MiB)

vif0.0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
          inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link
          UP BROADCAST RUNNING NOARP MTU:1500 Metric:1
          RX packets:390966 errors:0 dropped:0 overruns:0 frame:0
          TX packets:504382 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:106566736 (101.6 MiB) TX bytes:364483391 (347.5 MiB)

virbr0 Link encap:Ethernet HWaddr 00:00:00:00:00:00
          inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
          inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b) TX bytes:468 (468.0 b)

xenbr0 Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
          inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
          UP BROADCAST RUNNING NOARP MTU:1500 Metric:1
          RX packets:29276 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:3044564 (2.9 MiB) TX bytes:0 (0.0 b)