I'm not sure if something like that exists, but I've used
http://deviceanywhere.com in the past for Windows Mobile testing. This was before the iPhone, they're still around and have iPhone support, so it may be helpful.
Once I got everything configured, it was pretty sweet. It wasn't hard to setup either.
The one thing is, from what I recall, they were a bit expensive. But they have free trials.
I also found this article that could be useful:
http://www.softwarequalityconnection.com/2011/03/testing-app...
There's a bunch of options for testing without buying a bunch of iOS devices. They also have more DeviceAnywhere-type services listed as well.
I hope this helps.