The ambiguity regarding the two different single versions of "Baby Dont Forget My Number" is easily solved: The video version, in which Rob and Fab chase a girl's telephone number on a piece of paper throughout the streets of London, was the single version of the German and US releases. The UK release, far superior in my view, differed from the video.

Cue up your version, and here's how to check for the difference: In the video/US/German radio edit, the "Paid In Full" beat (sampled from "Ashleys Roachclip" by the Soul Searchers) kicks in on the chorus of "Baby! Don't forget...". In the UK version, the beat kicks in AFTER the chorus during the "I've been searching..." refrain. The UK version also removes the four bass stabs during both verses. This fingered bassline only kicks in on the third chorus.

Yes, there are two different "single" versions of this track.
The most common and very well known version (for example the YouTube video linked to some of these releases) is the album version of a length of 4:15...4:23 minutes.
The very rarely and real single version (in my opinion the better one) is of a length of 4:00...4:10 minutes.
I have both on mp3 and they really sound little bit different.
In any case the ~4:00 minutes version really exists.

A side "Baby Don't Forget My Number" length is actually ~4:22 - the same as all album versions. Does this ~4:00 minutes version exist at all ?
I have not found it anywhere, also not on any of the hit compilations from 1989 to 1990. All them have this same 4:17...4:23 version. Some 12" and CD maxi singles (for example Arista US and Canadian releases) suppose to contain both of them - maybe those owners can clarify tough.