I purchased a 32GB for my MT4G.  I thought it would be just plug and play.  When I go into settings it says size unavailable.  I synced all music through DoubleTwist but when I go under Media it says to insert SD card.  Do I have to format this SD card first?  What's the problem?

yes, you should always format new cards first, this places needed files in the root of the SDCard so the device can see it.. format via the device NOT a computer as well.

WIth the MT4G how do you format the card?  I'm new to the Android world.  Is it in the phone settings?

BTW it started working, apparently I needed to restart the phone.  But I still think its a good idea to reformat according to the phone, I just need instructions or how to do that.

Go to Menu, Settings, SD & Phone Storage. Now you have to press Unmount SD card, then you can format it, just remember to mount the card (which it should do automatically) after the format.

THANK YOU VERY MUCH!!!