Microsoft has a site for downloads of various software products, not just their own. It's called Windows ® Marketplace. For some time, people could download Ubuntu «Feisty Fawn» from this site. Later it was removed.
It's still available in Google cache.
Yesterday i decided to setup some jabber client on my phone SonyEricsson K750i. I found several J2ME clients availble on the net. I tried several ones and the one i liked more than others was Bombus
Everything was fine until i tried to setup GoogleTalk -- during connection Java threw an exception. Something about invalid certificate. That is, when usual pc programs warning you, it just threw an unhandled exception :( The good news are that the phone is aware of ssl certificates :) And you can install any CA certificate you need, even your own ones.
In case of GoogleTalk, its certificate signed by Equifax Secure Certificate Authority. To install it, you need to download its certificate in DER format and send it to the phone over bluetooth/usb/whatever.