If you're one of the remaining iPhone users clutching onto your original unlimited plan with either AT&T or Verizon, it looks like it might be the end of the road. When the new iPhone lands next week, it will come tethered to a new line of "shared" data plans with significantly higher prices--the closest thing to unlimited -- 20 GB on AT&T -- will set users back around $200 a month.

And that's the good news.

AT&T has already technically done away with its grandfathered iPhone unlimited plans, throttling data speeds when iPhone users top 3 GBs of monthly usage. It's not exactly clear whether iPhone 5 upgraders will be able to hold onto their so-called unlimited plans, but it doesn't really matter, since AT&T throttles 4G speeds, too, starting at 5 GBs.

Verizon has taken it one step further, announcing on its site that users switching from 3G to 4G will have to abandon whatever plan they're on and switch over to one of the new shared plans. Basically, the only way to hold onto your Verizon unlimited data plan and get an iPhone 5 is to pay full price for an unlocked phone. Per Verizon:

"You're not required to move to Share Everything, but if you do, unlimited data will not be retained on your line. ... If keeping unlimited is important to you, you can choose to upgrade and pay full retail price for the phone."

But if you're willing to fork over $650 for the iPhone, you don't actually need Verizon at all--T-Mobile's unlimited 4G plans start at $69.99. Of course, you'll have to unlock your phone to get it working at all.

All signs are pointing to T-Mobile USA again being left out in the cold when the sixth-generation iPhone is presumably revealed next week, but that doesn't mean the carrier won't have a strategy in place to combat the problem.

TmoNews is reporting that fourth-place U.S. carrier T-Mobile may soon be installing in-store displays to show off unlocked iPhones running on their 3G network in an effort to sell against Apple's forthcoming handset.

"All the intel streaming in seems to point to a 'bring your own iPhone' demonstration in store, which lines up perfectly with what T-Mobile’s been saying all along for their refarmed network," the report reveals.

T-Mobile is actively working to expand its network for 4G LTE, and in the process shift spectrum to radio bands that are compatible with the iPhone. While there are already plenty of unlocked iPhones that have retreated to T-Mobile, they've had to contend with slower EDGE data speeds due to this incompatibility.

The report claims T-Mobile store managers were "asked to activate a new micro-SIM before the end of August," which could point to the company rolling out the new initiative sometime this month.

With Apple now ready to announce their next handset on September 12, it appears T-Mobile wants to fight back by enticing iPhone owners to bring their device to the magenta network, which recently relaunched an unlimited data plan again.

Follow this article’s author, J.R. Bookwalter on Twitter