How do you test your mobile websites? Apps?

I'm fairly new to mobile development space. I had an issue recently in which my site wouldn't work properly on some devices. Seems something about my javascipt didn't work.

Regardless of the specific issue, it worked just fine on my Nexus, a BB, and iPhone 3GS and iPhone 4. But then we got reports from the field that it wasn't working on some other iPhone 4's (which is weird, yeah) and multiple Driod models (Verizon Android phones).

How do you test/manage your sites across different phones and platforms?

Our site needs GPS and data, do you buy sim cards and swap them between phones? How do you test Verizon? Are there big differences between T-Mobile Android builds and Verizon Android builds?

I'm looking for 'the best' way. We can afford to buy a few phones if that's the best way, but would like not to end up in a dozen contracts if I can help it.

Also, what do you use to measure client-side rendering time?