If it's a "Verizon" Xoom, you don't need a data plan to use WIFI, but if you want the data plan, you have to get a contract, it has different pricing for "mobile internet devices", cause it ain't a smartphone. It is much more expensive. I suggest, if you have wifi tethering, or *cringe* pay for wifi tethering, then I suggest not getting the contract. It won't add another line to your plan, it'll have it's own plan.
The Xoom does have an SD card, but not all xooms have the OTA update to support it, 32gb built in is alot though, unless you're a packrat, then it may be a lil cramped. Assuming the press release taht they will start updating xooms to 4g in the summer, only then will you be able to use 4g and the sd card slot.
Currently, the xoom has been updated to Android 3.1, so it has support for Music Beta, USB host devices, resizable widgets, etc (more here
Android 3.1 Platform Highlights | Android Developers)
In the end it's up to you, do you want an Ipad, or a Xoom, personally, the xoom has way more functionality in the real world, get the Ipad if you just want entertainment, and no real use. I recently helped my coworker decided whether to get an ipad or a xoom,a nd she bought the Ipad. Now she can't go on her work website at all (requires flash and java), she hates the ****ty camera, she can't sideload downloaded apps, she hates the calendar app, she can't share the ipad because it has no user profiles, and she hates the screen ration, cause she watches movies all the time, 16:9 shrunken down isn't fun....
I know I should've convinced her more to buy the xoom instead, but sometimes, people don't care.
