According to a supposedly ‘leaked’ document from a T-Mobile training, it appears that T-Mobile will begin offering an unlimited mobile to mobile service starting April 4.

A photo of a training document, published by TmoNews, indicates that the unlimited mobile to mobile minutes will add $10 to current subscriptions. It does not require a contract extension, and does not require a commitment to keeping the add on option. It can be added or removed without penalty.

The mobile to mobile coverage will include calls to all US domestic (including Puerto Rico) mobile numbers on any carrier’s network. According to the document, more than 80% of calls on T-Mobile are made to mobile numbers. The training recommends that agents ask customers who have experienced overage costs if they would like to learn how to get the unlimited calling option.

The new offering from T-Mobile may allow the carrier to be more competitive with Sprint, who already offers an unlimited service, and AT&T, who offers a $20 unlimited texting and unlimited mobile to mobile subscription add on.