MT3G Slide owners, you won't believe your eyes today. April Fool's has passed, and T-Mobile is not trolling you - the Froyo update is indeed available for the poor younger brother of the original myTouch 3G which already received Froyo almost 6 months ago. Don't let the name fool you, as there are, apparently, quite a few differences between the 2 devices - enough to tie up the release for such a long time.
The update is not over-the-air (OTA) - you will have to download it from HTC's servers, which are coincidentally on fire right now, barely pushing out the file at 6-7 KB/s. Considering there are over 150 megabytes to go, you may want to leave it downloading overnight and watch the whole Star Wars hexology (yeah, that's a word).
Oh, and you'll need HTC Sync 3.0.5511, also available at the source link, which in itself weighs almost 70 MB. See you in 3 days, guys.
Update: TmoNews commenters are offering faster mirrors: