which ipad mini specs best for VOIP?

Hi!

I'm shopping for a mini ipad to use with VOIP provider.

I just ditched AT&T. Anyone know what ipad specs are best to match with VOIP?

I know bluetooth is good.

I will no longer be with one of 4 US carriers, so not sure how to buy?

I want to sync with Iphone 4, Google Chrome, Drive, other apps, etc.

I appreciate any and all info. Thanks!!