The T-Mobile G-Slate is in the midst of getting an OTA update to version 10p, which will bring security fixes, USB controller support, and a fix for an Android Market (Google Play?) update problem. It's not Ice Cream Sandwich, and at first glance it looks like it will be based off Android 3.2. All we're sure about at this moment is that it's version 10p.
Worth noting that you'll need to clear data on the Download Manager app to install the update, which the notice screen reminds you to do before installation. Be sure to back up any files you may have sitting in the Download Manager, just in case they too are deleted. You'll also have to have your G-Slate charged up before you can continue.
If you're one of the few who picked up the G-Slate, now would be a good time to check for updates.