VALAALUNLTT, sounds funny when you try to pronounce it. It actually breaks down like this:
Simple Choice - Your plan name
AAL - add-a-line
UNL - Unlimited
T+T - Talk + Text
If you are seeing this on your bill, you most likely have a family plan with more than 2 lines as lines 3 and above are coded with that specific acronym. Lines with this acronym have unlimited minutes and messages and would have an additional feature if you added data to that line.