The Street reports T-Mobile is aggressively leading the way to lower monthly service rate plans for smartphones in the United States. The carrier, which is ranked the fourth largest carrier in the United States, started the trend with competitors AT&T (ranked second), Sprint (third) and Verizon (first). Being left with no choice, these rivals have reluctantly followed suit.

T-Mobile's effort was rewarded with concrete results almost immediately. After offering discounted plan pricing in 2013, it added customers for the first time in four years. Currently, T-Mobile is ready for another tweak in its offerings, again forcing competitors to respond.

Last week, T-Mobile announced that it will double its high-speed Internet data and 4G/LTE, while the monthly fees remain the same. This means that a customer that pays $50 a month, and gets 500 megabytes of 4G data will jump their data limits to 1 Gigabyte of 4G LTE. This will take effect March 23.

Furthermore, T-Mobile added unlimited international texting from the United States to most countries globally. This is on top of its unlimited talk and text plans.

As for increasing prices, T-Mobile does that too. It raises some prices, but this applies to new plan subscribers only, not to the existing customers. For example, a customer who currently gets unlimited 4G/LTE data can opt to keep their additional $20 a month pricing. However, new customers will pay $30 a month for the unlimited LTE data and 5 GB of wireless tethering.

Regarding T-Mobile's rivals, AT&T adjusted some of its plans and reviewed some contracts, while Verizon Wireless sees it fit to offer new deals too. Its "Share Everything"-plan has an attractive offer now called "More Everything."