Rumors seem to be true. Future T-Mobile customers have a good deal to look at. The carrier is offering free mobile phones if you sign up for group calling plans at its retail store on Saturday. A promotion that has reached the headlines of major newspaper and blogs.

T-Mobile new customers will get absolutely free handsets of choice if signing for a group plan which is a calling plan that has at least two users. Existing T-Mobile customers can benefit from this new offer, if you switch a single-user plan to a so-called family plan and add at least one user.

The mobile operator will offer you up to five free phones with a single group plan, however, each is available with a two-year contract. According to Fox News, T-Mobile’s offer was already in the works before the carrier knew that the new iPhone version will become available.

Not all phones are for free, however. T-Mobile says that Android-based handsets including HTC myTouch 3G Slide which is available for $180 with a two year contract and rebate, or Garminfone that comes for $200 with a two year contract and rebate, will require a mail-in rebate. Details are missing at the moment, but you will most probably find all the information needed at your local T-Mobile retail stores. Nevertheless, the promotion sounds quite tempting.

T-Mobile currently has 33.7 million customers, as reported at the end of the first quarter, but will it increase with the current offer?