I recently had the very same question for my Cisco rep (we were hoping we could keep our existing domain) and here is the response that i got back as to why you really should use a new one. hope this helps...
Although this is mentioned in the FAQs, I want to help call out some very important details:
• I recommend to select a new site URL. This will be the smoothest option. Otherwise, using your existing site URL will require about a 2-week site downtime to be recreated (meetings, recordings, and host list lost), because it can’t be “migrated,” so don’t fill out the standard migration form; that will cause issues because it will prevent you from having Common Identity (single place of Spark/WebEx user management).
• In addition, CUWP Cloud does not include Messenger (Connect & Jabber), so cancelling your existing site cancels the whole bundle (including Messenger). Some partners need more time to make that change, so they are using a new site URL for CUWP Cloud and keeping their existing site active (on old platform) to allow time to create the host accounts on the new site and decide how to transition off Jabber and begin adopting Spark. I understand Spark currently doesn’t have all the same capabilities as Messenger, but CUWP Cloud is promoting Spark.)
• Keep in mind if you already have toll-free audio and international dialing, that is not included with CUWP Cloud, so moving your site to annuity will deactivate that from your site. Toll Named User is free with CUWP Cloud. But that does not include call-back feature. If you want call-back feature. You will have to do an add-on to your order and purchase TNU+ (which is toll named user with call-back feature). It will be at your partner discounted rate. If you need international dialing, you’ll need to purchase TNU+International. When selecting these audio options, you have to purchase that audio option for all licenses. (i.e. you can’t have 50 people on TNU, 50 on TNU+ and the remainder on TNU+International.)
- You may see an option to “override URL” when entering your CUWP, Cloud provisioning information. DO NOT PRESS THAT BUTTON, select a new URL. The ‘override” selection will cause you to have to cancel the order and re-order.
- You must select Internal Business Use as intended use in your order.
- No discounting beyond your partner standard discount is permitted.
- When ordering, it's very important that the Spark admin email (if you already have Spark from early field trial) is the same exact Spark admin email for the order.