I have Google Voice on my G Slate (grabbed the app from a Xoom site) and it works fine (you need to get a Google Voice number) but I wanted to send/receive my texts from my G2 phone number so I also grabbed the app Sync SMS for tablets over at the xdadevelopers http://forum.xda-developers.com/show....php?t=1010597 and it is working great so far.
The slide it application is a great substitute for swype... That wasa big thing thati missed at first, even though there isn't texting on the Slate because it was kind of a pain to type anything of length one letter at a time.
So... I added my GSlate number to my GV. No love. So I took my sim card out and put it in a tmobile phone and imagine my surprise when GV tells me this is a PRE-PAID phone number! ARRRRRRGH! Apparently GV does not work with pre paids. XDA forums has an APX that I tried and it looks REAL good except.... I still need to get GV to recognize this number as a contract number not a prepaid number.... ARRRRGH!
went to a tmobile store and they tell me its a postpiad/contract number.... whatever the issue using the apk referred to above, GV is working like a champ. there is still a noticable delay but its working.
interesting... the Optimus Pad, in the UK, did come with a text messaging app. Not one I'd seen on Android before. Of course, it's not associated with a mobile provider anyway, but I was certainly able to put in a SIM and use it to send texts.
I would love to be able to at least text from the number at to my G-Slate data line. For now I am trying to use Google Voice and/or Google Talk instead.
As for keyboards to allow you to type more easily on the tablet you MUST try SwiftKey Tablet X. This has transformed the G-Slate typing experience into something significantly better than any other tablet keyboard can offer.