So I work for Verizon Customer Service (I know that might make me "the enemy" in a lot of people's books) and I thought I'd try and explain the activation vs suspension issue.
First off, if you want to see if you got charged an activation fee, the best way to check is on myverizon. log in, click on View Bill. the activation fee will be listed under 'Charges by Line' for your new device. to see if you were credited for it, meaning it got waived in store or by customer service, it would be under 'Billing Summary' in the "Verizon Wireless' Surcharges and Other Charges & Credits" portion. On a paper bill, the activation charge would still be under the new line and the credit would be on page 2 under 'Other Charges and Credits'. Activations are usually waived as promotions or as part of an employee discount.
As far as suspension goes, if you suspend a line(phone or data) online or in the automated phone system, theres no $15 charge. if you call and have a rep do it or go into a store and have the rep do it, you will get charged (unless its a lost/stolen suspension, which are waived). You can have your line suspended with or without billing in blocks of 90days. Without billing means you have no monthly charge but if you are under contract, that contract will be extended by the length of the suspension which also pushes back upgrade dates. You can do that as often as you like as long as it is less than 180days in a 12month period. With billing means you still pay for it but you cant use it, typically only used if its under contract and its for short term, ie parents punishing kids.
So if you aren't under contract on your Xoom and you want to switch 3G service on and off, suspending without billing would be the option you want to use up to 180days per year. If you are under contract, you could also do that but keep in mind that it will push your contract end date out.