If you deploy any of the three mobile configuration types and they are deployed appropriately, you do not need a mobile XML sitemap file.

In fact, Google’s John Mueller said you should NOT have a mobile sitemap for mobile sites. The only case you should have a separate mobile site is when you have a feature-phone (WAP/WML, etc) version of your site, which is something most people don’t bother with these days.

But for an ordinary mobile-friendly web site, no new sitemap is needed or wanted. It can actually cause more confusion if you add a mobile sitemap file.

Google’s John Mueller said this in a Google Webmaster Help thread:

It is rare to see John call something out as 100% “wrong,” but here he did.

It is interesting how logic goes out of the window for so many SEOs.

Forum discussion at Google Webmaster Help.