[kroewe]

i have posted once before offering the solution of using SSMaHo as a means of using a different application for SMS.
it does require a bit of set up and reading the instructions on the first few posts...but it lets you change almost any link in sense...i use it to open smschat when i click on a msg or on the all message softkey on my sms tab, and to open funcontacts when i click all contacts on the people tab. i also use it to open resco photo when i click on albums on the photo tab and used to open weatherbug when i clicked the weather on the home tab, but cookies 1.7 now takes care of that one.
i know its not exactly the solution you are looking for, but it works, and i am sure instead of smschat you can use it to open WM sms if you know the .exe and cmd.

link to xda for any interested. i am on sprint stock 6.5 and it works perfectly for me...

http://forum.xda-developers.com/showthread.php?t=493810