If you happen to be a T-Mobile customer, the carrier looks to be introducing an unlimited calling plan. Starting April 4th, “T-Mobile will offer a Unlimited Calling To Any Mobile, a $10 per month subscriber-level feature that includes unlimited calling to any local mobile number, including Puerto Rico, regardless of the carrier.”
This is a very similar plan owned by T-Mobile based in the UK which is called “TheFullMonty” Plan.
A leaked document acquired by TmoNews says:
If you’re a current T-Mobile customer and love to talk, you can add this to your plan without extending your contract. In addition, it doesn’t affect your current plan in any way, meaning you can add or remove the new Unlimited Any Mobile whenever you want. While T-Mobile does offer unlimited plans already, this is a great feature for folks who don’t need the minutes year round.