U.S. Cellular has sold 10 MHz of its wireless spectrum to T-Mobile for $308 million in cash. Reuters

As smartphones proliferate, many carriers have taken the opportunity to profit with pricey contracts that seem to cost much more than they are worth, but there are still a few ways consumers can get the upper hand and lower monthly costs.

Many have been discussing a T-Mobile pre-paid plan that seems to be the stuff of a customer's dreams: unlimited data on a smartphone for just $30 a month. Danny Sullivan of CNET recently discovered the plan on T-Mobile’s pre-paid website. It offers 100 minutes of talk, unlimited text and the first 5GB of unlimited data at 4G speeds. This plan, as Sullivan and many others have noted, is ideal for those who don’t use their smartphones for much talking but consume a lot of data with frequent Internet use, streaming and downloading. While data speeds do get throttled after 5GB, even heavy data users would have trouble using up that allowance.

T-Mobile $30 Unlimited Data: How To Get It

T-Mobile does a good job at keeping this option well hidden. Customers won’t find it on the network’s main site, which advertises a Simple Choice non-contract plan that starts at $50 per month for only 500MB of 4G data, but if you go to T-Mobile’s pre-paid website, the aforementioned plan is listed under Pay as You Go. Scroll down to the bottom of the page to find the hidden gem.

This is where things can get tricky as there are several caveats to getting this plan for smartphones. First, the plan is available only for new T-Mobile activations, meaning that a current T-Mobile customer may not be able to switch their number to a new plan easily, and may be subject to termination fees of some sort if they attempt to switch plans. We will touch more on this later.

In order to sign up for the plan, customers must their buy a phone or buy a SIM card. While devices newer to the market are not available under this option, many older high-end smartphones such as the Samsung Galaxy S2, Galaxy S3, Galaxy Note 2 and the Google Nexus 4 are available for purchase. Customers who happen to not want a smartphone can also choose from several less expensive feature phones or can buy a pre-paid device from Walmart. Customers who already have a compatible phone can simply buy a SIM card for their device.

Once the phone or SIM card is in hand after one week for shipping, customers will be able to continue the activation process online, where the $30 per month of 100 minutes of talk and unlimited text and data option should be available. After activation, the device should work under the purchased plan. Be advised that this plan is available online only and customers cannot get this option in stores. The plan is also subject to disappearing at any time, especially if a significant amount of customers begin to use this option, but for now it remains available.

T-Mobile $30 Unlimited Data: Customer Reactions

Sullivan notes that the plan falls under "you get what you pay for," with service quality being decent for his location in Duluth, Minn.; he was able to start a new activation for his already owned Google Nexus 4 smartphone. Areas where T-Mobile coverage is more widespread may receive better service. Nate Swanner of Android Authority also notes that T-Mobile service is not strong in certain areas and recommends using Open Signal Maps to see what the carrier’s coverage is like in your area before considering this, or any new plan. Additionally, T-Mobile’s 4G LTE coverage is currently available in seven cities across the country, so this plan may not be an option for those for whom 4G speeds are imperative.

T-Mobile $30 Unlimited Data: How To Skirt The Rules

Now, let’s get back to the new activations stipulation for this plan. While the simplest way to get this plan is through a completely new T-Mobile account, this does not mean that current T-Mobile customers are fully barred from getting their current devices on the plan.

Chris Morran of Consumerist spoke to a T-Mobile representative who explained that any T-Mobile postpaid subscriber who is “out of contract, or any other obligation,” would be able to switch to the $30 plan by purchasing a prepaid device kit from Walmart or a SIM card from T-Mobile and having T-Mobile do a rate plan change on the existing account.

But a T-Mobile prepaid representative told IBTimes that an existing T-Mobile customer within contract would not be able to cancel their contract and start a new contract with same device as the $30 plan is more or less a Walmart exclusive. However, Swanner has figured out a method of activating his Nexus 4 with the plan despite being an existing T-Mobile customer. While the plan requires a new activation with a qualifying phone, that doesn’t necessarily mean that customers have to use the device with which they activated their plan; they can easily switch out the SIM card to a device of their choosing.

What Swanner did was buy a cheap prepaid phone from Walmart and activate the SIM card. Then he went to a T-Mobile location and asked for a micro SIM card that was compatible with his Nexus 4. After T-Mobile activated the micro SIM card, with his recently activated account transferred to the compatible card, Swanner was able to install the micro SIM card into his Nexus 4 and have it work under the account intended for the prepaid device from Walmart. While he ultimately donated the pre-paid device he bought to charity, Swanner does not indicate what he did with his existing T-Mobile account.

T-Mobile $30 Unlimited Data: Exempt Devices

Since the plan is connected to the Walmart prepaid device kits, we expect that T-Mobile won’t stop offering it any time soon; however, that doesn’t mean that it isn’t subject to change. T-Mobile’s website notes that compatible and unlocked devices are required for this plan, and a compatibility search can be found under the bring your own device section of T-Mobile’s prepaid website.

Many of the most recently released devices such as the Samsung Galaxy S4 and the HTC One are not currently compatible with this plan; however, T-Mobile notes that devices are added for compatibility as they are approved, so those devices may work soon.

Swanner expects that devices such as the HTC One and Samsung Galaxy S4 Google Edition should be compatible with the plan as they will not only be GSM-unlocked but will also be almost exclusive to T-Mobile; the only other network that will carry the devices is AT&T.

Many consumers should have no trouble being compatible with the stipulations to this plan, and may not even have any problem if their service is not perfect. In a market where keeping up with the latest smartphones is extremely taxing to the wallet, we imagine many savvy smartphone owners will at least consider this inexpensive option.