Best app for free calls android to iphone?

[01steven]

My wife is currently in the UK and is using a ZTE Blade running Android Froyo 2.2
I am in the US with an iPhone 4.
We both have unlimited data packages.

What is the best app for us both to run to enable us to make free calls to one another AND ALSO for the phone to ring / notify us even if the app is not running or only running in the background.
In other words for it to work just like a normal phone.
I know skype doesn't push new call notifications on the iPhone unless the app is actually running.

 

[Jalarm]

Google voice, easily the best, also you get free text.

 

[01steven]

Google voice, easily the best, also you get free text.

Will it work in the UK?
She has a US Google voice number from her US-based Google account, but I didn't think it would work in the UK. What are you suggesting? That she call my Google Voice number? Or my regular cellphone number?