Yes it is, Microsoft Portrait is an example application that uses the SIP
protocol to detect presence and allow for IM capability on the PocketPC. This
works in conjunction with Microsoft Live Communications Server (LCS). You
could also use the MSN Messenger library on the device to leverage the more
publicly available MSN Messenger Server.
To Recap, it is possible to leverage LCS presence and IM capability on your
device using the Compact Framework by leveraging Microsoft Portait or
implementing a SIP client, you could also use the Messenger API.
Also, because the .Net Compact Framework support socket communications you
could in theory create your own listner on a server (using the full .Net
framework) and a client on the device (using the CF). This way using TCP
classes available in both framworks you can create your own chat or
messaging application.
Hope this helps.
Yves.