Well, you can't get one with just data. No company will do that, at least in the US. They're not going to let you forgo their profitable phone service for their equally-profitable-but-far-more-used-therefore-we-don't-want-you-to-use-it data services.
And some terms and conditions pages will tell you that you're not allowed to use their data for VoIP.
Cheapest yearly price in the US is $495 a year from Straight Talk. Unlimited calling, unlimited texting (you won't need it; iMessage), and "unlimited" data. Conflicting reports about the latter. But they also have the most draconian data use policy and are prone to just cutting off your service without warning. Also it's AT&T's network and there's no LTE.