Recently I've seen quite a number of people selling "unlocked CDMA phones" for use with a variety of carriers, and listing Revol as one of them. As an employee of a Revol Authorized Retailer, I feel it is only fair to warn you of a couple of facts.
1. Revol will only activate a Revol phone once their software is loaded. That is to say that if it wasn't originally sold by Revol or one of the Authorized Retailers it will require one to have an software "upgrade" done, available at Revol corporate store locations and certain Authorized Retailers. However I would still recommend contacting them prior to purchase to be sure that model is supported.
In the past, Revol would only activate a phone with its serial number in the Revol master database (sold by them) - no exceptions.
2. Not saying that any phones I've seen for sale here on eBay have been, but if a phone on the Revol network is ever reported lost or stolen, that serial number has become null and void forever and the phone can never be activated. Before buying any Revol phone, contact the seller and get the 11 digit ESN serial number (decimal not hex) and using this check with 1-800-REVOLHQ (or the local customer service number in cities within coverage) to be sure that the phone you are looking to purchase has a free and clear ESN#. The ESN number is on the outside of the original packaging, or on a sticker underneath the battery in the rear compartment.
By taking a few simple precautions you can ensure that any phone you do purchase can be used with the Revol network.
*** EDIT ***
Since writing this, Revol has now begun to activate phones from a selection other CDMA carriers. Bullet point #1 has therefore been upgraded to reflect these changes.