T-Mobile is launching a limited-time offer of $100 per month for unlimited talk and text plus 10GB of LTE for four lines.

In a blog post, T-Mobile CEO John Legere gets in his customary shots at AT&T, calling the carrier’s similar plan for $160 a “joke.”

But there are some key differences between the two offerings. Where AT&T will allow fewer than four lines on its plan, T-Mobile’s offering is only available for four lines. And those four lines each get 2.5GB instead of sharing a pool of data, allowing some users to chew through more data than others on the same plan.

Macquarie Capital last month revealed first-quarter data usage averages showing the typical T-Mobile subscriber was blowing through more than 2.5GB in a month.

But T-Mobile customers who go past the 2.5GB in this plan won’t be charged overages like they would on the other three big carriers. They’ll just be throttled back to slower data speeds. Customers who opt for the T-Mobile offer will also get unlimited international text and data and won’t have data rates apply to their music streaming from services like Spotify and iTunes Radio.

T-Mobile isn’t the only carrier working to undercut the popular 10GB plans from AT&T and Verizon. U.S. Cellular in May announced an identical offer going for $140 per month.

The offer from T-Mobile will be available June 30 through September and customers who sign on will get the special rates until January 2, 2016.

Credit: T-Mobile