As AT&T prepares to head into the regulatory review of its pending purchase of T-Mobile USA, the telecom giant’s CEO has stated, however noncommittally, that existing T-Mobile customers should not see their rates go up. And according to a comparison done by our number-crunching cousins at Consumer Reports, many of those T-Mobile customers will be saving between $15 to $50 per month for similar service.

From Consumer Reports’ report:

T-Mobile charges $50 per month for its basic 1,000-minute individual Even More Talk two-year contract plan, while AT&T charges $60 per month for its nearest equivalent Nation contract plan, which includes only 900 minutes. If we adjust for the difference in voice minutes, AT&T costs $16.67 more per month or $200 more per year for a comparable monthly allocation of minutes.

The more you buy, the bigger the price disparity. T-Mobile’s two-line, 3,000-minute Even More Talk + Text (unlimited messaging) + 200MB data two-year contract plan for smart phones costs $140 per month. The closest AT&T FamilyTalk Nation plan costs $170 per month, after you add data and messaging to the base price, but delivers only 2,100 voice minutes.

Adjusted for the 900-voice-minute shortchange, this AT&T plan costs $50 more per month or $600 more per year.

A rep for AT&T points out that this math doesn’t factor in rollover minutes, which AT&T offers and T-Mobile does not.

If AT&T is truly going to allow T-Mobile customers to continue on with their existing plans post-merger, some current AT&T customers may want to consider the possibility of jumping ship early to a T-Mobile plan so they can be grandfathered in.

However, there is the caveat that these grandfathered plans are usually voided when you make any change to the plan.

Writes CR’s Jeff Blyskal:

So, we reckon, if you get married after the AT&T takeover and need a family plan without changing carriers, that won’t be just a tweak to your individual plan: You’ll be shopping for an AT&T family plan. Need to increase or decrease your minutes or trade up from a standard phone to a smart phone with required data service? Welcome to AT&T.

In other words, if you make any significant change to your T-Mobile plan, you’ll be forced to “Rethink possible,” as AT&T’s current marketing slogan presciently warns shoppers, and you’ll likely lose access to today’s relative thrifty T-Mobile plans.

CR analysis: T-Mobile is cheaper than AT&T [Consumer Reports]

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