okay guys, i'm not even on OS 3.0 yet so i cant test this myself so im asking someone to experiment for me here (im not liable for your damages ;p)
i remember when i couldnt get swirly to work i had to go to this website to get tmobile to send me some settings directly and then it got me going with swirly.
the site is:
T-Mobile Wireless Data Configurator
follow these steps:
1. click begin, choose sony erirsson for manufacturer
2. choose W800i for handset
3. select Picture Messaging (MMS) as the service
4. fill in the captcha and your mobile number and click send configuration
now when i did back in swirly, it sent an mms with some config settings and swirly asked me if i wanted to use those configurations, i clicked yes and it did some stuff automatically and got swirly working for me
im not sure how the MMS will show up with the intergrated SMS/MMS app in 3.0 but its worth a try
i'll probably be loading 3.0 onto my phone tomorrow so i'll test it out myself and update my post with my findingss