People forget something important.
A lot of new customers means T-Mobile can get more towers in order to expand their coverage to attract more business. However, a lot of customers aren't going to inspire AT&T or VZW to stop their insane business practices, in fact the opposite is true.
A lot of customers for T-Mobile will mean AT&T and Verizon will have to step up to compete.
If they increase the price to maintain profit, they will see more customers flee.
If they decrease the price, they will retain customers.
Look at Sprint. It lost a lot of customers to T-Mobile in the past year. What did Sprint do? It lowers the price and imitate T-Mobile plans.
It is only 7-10 lines that get you the $25 per line per month deal.
T-Mobile USA offer better deals with 5 lines at $22 per line, though it only has 500MB vs 1GB on Sprint
1st line: $50
2nd line: $30
3rd line: $10
4th line: $10
5th line: $10
$22 per line at 5 lines
Each line will have unlimited talk, unlimited text, 500MB of LTE and unlimited 2G
+ $10 to any line to upgrade to 2.5GB of LTE data
+ $20 to any line to upgrade to unlimited LTE data
Cost per line: 1 line, 2 line, 3 line, 4 line, 5 line
Sprint:... $55, $50, $45, $40, $35
T-Mobile: $50, $40, $30, $25, $22