Issuing stock is not free it's a lot more expensive than spending cash. That's basic financial theory. Issuing stock is the most expensive way to pay for something.
five year from now VZW will have a fully built out network and AT&T will be relying on T-mobile, the 4th player in the game, for its future.
How do you know AT&T is paying for the stock issuing?
And like I said, AT&T has been planning LTE. I doubt T-mobile's current "4G" will even be a factor by then.