I gave away my 3870 to my elder daughter when I got the 5555, but I think I had Skype running on it.
I certainly do on the 5555. Daughter never used the 3870 and granddaughter "acquired" it and then "lost" it. Skype on the 5555 works passably well - the Laptop does better, but if there's a WiFi hotspot about I can Skype with either.
Mine has Windows CE 4.2 on it. The label on the back says "Pocket PC 2003 Prem w/ Outlook 2002". I have no idea if that's WM2002 or WM2003, but it does all I want it to do! Diary, phonebook, very occasional e-mail or web browsing, and some very large Excel spreadsheets (including the details of the 4,600 burials in our Churchyard).
I used to use it for SMS, via Bluetooth to the old cellphone, but the V3 made that superfluous and I don't use it any more.
If you want me to Skype you from my iPaq, PM me with a Skype name.