Can't vouch for it at all, we just ended up doing mobile testing manually. Good excuse for a company provided iPhone. [img]/images/graemlins/smile.gif[/img]
Comes down to what you're testing. Just accessing websites designed for a phone? You can sort of fake that out for some basic testing by switching user agents(something I do with Selenium and Firefox). But if you're testing apps you're not going to get that done with QTP for sure.
Now, you might want to take a look at SeeTest by Experitest.com, they have a tool to automate mobile devices with plugin support for QTP. I'm not affiliated with them.
If you like what they offer and want to go the cheap/free route, look into Sikuli.org, a free equivalent. But this tool is Java and Python based, meaning more work to integrate with QTP. These articles on Sikuli may help for mobile device testing:
I have a friend who has managed to get fairly good results automating apps on mobile phones with QTP. I've seen his framework run against iphones, androids, and blackberrys.
I don't think he'd be too happy with me if i told everyone how he pulled it off but if you want to get more information on it, send me a PM. I think plugging his company in this post would violate the advertising rules of the forum.
I have used seetest and I found it more useful. My requirement was to test the same app for Windows Phone as well as for Android. Seetest uses the same script to test it on multiple platforms and I found it quite useful as it saved me a lot of time.