T-Mobile gearing up for free phone promo on family plans next weekend?

So it looks like T-Mobile has something special in store for Father's Day, and if you've had your eye on any of the pricier gear like the HD2 or the myTouch 3G Slide, this might be a prime opportunity to get in on the action. TmoNews has scored what appears to be a script for a commercial that'll be airing ahead of the 19th, whereby you can get any phone in the store for free on one day only by switching to a family plan. What's not clear is whether you'll need to add another line when you make the switch, but we'd imagine -- some of these phones are crazy expensive off-contract, and just like any of the countless BOGO offers that Verizon likes to push, there's no such thing as a free lunch. Still though, if you were looking to add a line for the fam anyhow, this'll likely be the cheapest way to do it.