calling Ajax-derived telephone numbers in iOS javascript

Previously I mentioned a little demo iOS app that just wrapped a web widget. Part of the demo was to pull down a phone # from the server via an Ajax call and let the user try to dial it. This seemed to run afoul of Apple's "user initiated action" type of rules... my code worked if I triggered it from a button directly, but if I tried to make the call as the result of an Ajax call, no dice. 

Problem was I was using 

window.open('tel:######'); 

-- turns out doing 

window.location = 'tel:######'; 

face no such restriction. 

Phew! I was worried I was going to have to build a button and have the user press that one, too.