T-Mobile is firing another shot across the bow of the wireless industry with a new plan aimed at the budget-conscious.

The Simple Starter plan, as it is called, costs $40 a month and provides unlimited talk and text and 500MB of LTE data.

Calling the value plans from other carriers "bait and switch" because they promise low fares but automatically charge users exorbitant data overage fees, T-Mobile proudly trumpets the fact that Simple Starter customers won't be automatically charged for going over their data limit.

There's a catch, though. Most T-Mobile plans don't cut you off when you run out of 4G LTE data, they just drop you back to the HSPA+ network, with slower speeds. The Simple Starter plan doesn't quite work that way. When a customer runs through the 500MB of included LTE data, a message pops up prompting them to buy more data: either 500MB for the day ($5), or 1GB to be used over the next week ($10). So, while Simple Starter is not uncapped, it doesn't land you into trouble with automatic overages. Simple Starter customers also don't get the free international texting and data offered to customers on Simple Choice plans (which start at $50 a month).

The Simple Starter plan is indeed eligible for the program where users can get up to $650 per line by switching to T-Mobile (up to $300 to trade in their phone, and $350 to pay off the early termination fee from their other carrier).

This is the first of three days of announcements promised by T-Mobile.