I don't think you need a modification to do it. It needs the network to have it.
I'm not sure of any of the networks have volte working yet. That's why the N5 drops to 3G for calls.
Edit: After some reading it appears you'd also need an update from the carrier. T-Mobile just turned theirs on in Seattle.
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Last edited by NaterTots; 27th May 2014 at 10:34 PM.