With an acquisition by AT&T, Inc (T) seemingly impending, many customers of Deutsche Telekom AG's (DTE) T-Mobile USA phone carrier are already jumping ship.  T-Mobile USA yesterday announced new pricing that may give some a bit of extra incentive to stay, while giving others all the more reason to jump ship.

I. The Cap

The bad news is that T-Mobile has officially killed its "unlimited" data plan.  In that regard T-Mobile is following in the footsteps of AT&T, who ditched unlimited data plans last June.  

Verizon Communications, Inc.'s (VZ), the nation's largest carrier (before the T-Mobile merger closes, at least) with 104+ million subscribers will also phase out its unlimited data plan this summer, and has already started capping data usage on its 4G LTE network.  Like T-Mobile, Verizon will pad this blow with new family options.

T-Mobile's new tiered data plan offers 200 MB for $15 USD/month or 2 GB for $20 USD/month.  T-Mobile's tier extends higher, though with a 5 GB per month allowance for $30 USD/month, or a 10 GB allowance for $60 USD/month.

Rather than imposing overage charges, T-Mobile is merely bumping the offender's connection down to 2G and letting them languish at slow data speeds until the billing quarter is over or they pay to upgrade their data plan.

To be fair, T-Mobile's "unlimited" data might not have been so unlimited after all.  The carrier was caught last August throttling its unlimited plan connections and sued in California court.  After the news broke, T-Mobile confessed that it indeed intended to throttle "unlimited" connections if they were used past 5 GB.

II. Family Plans

To soften the blow of killing unlimited data; T-Mobile is unveiling some pretty competitive family deals.  

Individual plans currently have tiered pricing for voice allowances of 500, 1,000, or unlimited minutes.  The new family plans will have voice allowances of 1,000, 2,000, or unlimited minutes.

Similarly, the individual plan offers unlimited texts for $10 USD/month; the family plan will offer unlimited texting for $20 USD/month.  Similarly, the data plans cost twice as much when shared on a family plan.

A family plan starts with 2 lines, but costs $10 USD/month to add more lines.  Up to 5 lines can be on a single family plan.

The results are a fairly competitive pricing scheme that narrowly beats AT&T in pricing (for example, family plan texting costs $30 USD/month on AT&T).  It still remains to be seen how the plan stacks up against Verizon's updated rates, which it plans to unveil this summer.

III. 4G Where Art Thou?

We've said it before and we'll say it again, no matter how much T-Mobile wishes it, its "4G" isn't true 4G.  Rather its a 3.5G tech (HSPA+) rebranded by clever marketers.

T-Mobile's HSPA+ network fails to deliver the full speeds promised by the HSPA+ specification, much as current true 4G wireless networks from Verizon and Sprint Nextel Corp. (S) do.  But as the base HSPA+ spec is significantly lower than the 4G spec, real world imperfect HSPA+ generally is slower than real world imperfect 4G (LTE, WiMAX).

T-Mobile's pricing certainly makes it more attractive than AT&T, who is also putting off the upgrade to true 4G, opting to rebrand its own HSPA+ as 4G as well.  But the plan may seem less attractive when Verizon unveils its own pricing on true 4G data.

IV. Sprint -- The Last Hope

All the market movement leaves Sprint as the last hope for unlimited smartphone data.  

Sprint is arguably the best deal on the market, offering unlimited talk, text, and data (+4G) for $99.99 USD/month.  

In many regions you'll pay at least $35 USD in local taxes and fees, so your real world phone bill with Sprint will end up at around $135 USD/month for a connection with 4G.  By contrast a non-4G, 10 GB capped connection, with fees will be around $155 USD/month on T-Mobile ($120 USD/month pre-fees).

T-Mobile's family plans also look even more miserable in the face of Sprint's.  At 2-line unlimited talk, text, and 10 GB data family plan without 4G will cost you $220 USD/month pre-fees on T-Mobile.  That same plan will cost you $190 USD/month, pre-fees on Sprint.

So Sprint’s plans give you unlimited data, true 4G access in some reasons, and cost $20 USD less for individual plans and $30 USD less for family plans.

But if you needed any more incentive to ditch T-Mobile, Sprint is offering $125 USD to customers who switch from a rival carrier.

All of this sounds somewhat like an ad or promotion, but it's just the plan facts -- Sprint is far and away the most affordable carrier and the only carrier to still be fighting the good fight with unlimited data.

Now there are a couple caveats -- in some regions Sprint's network isn't quite as strong as Verizon and AT&T (the same could be said of T-Mobile).  Note that in some areas the reverse is true, but nationwide AT&T and Verizon tend to be strongest in coverage.  Also Sprint's executive leadership has suggested that they may impose data caps at some point, though for now they're content to leave their connection uncapped.

Sprint current has only 51 million customers, far less than the 129.8 million that T-Mobile + AT&T have and 104 million on Verizon.  But it would seem likely that some customers at least who had stuck with T-Mobile for the free data may jump ship to Sprint.