A growing number of smartphone users — especially younger folks — almost never use the “phone” part of their wireless device, but many of them have monthly plans that include a ton of voice minutes they will never exhaust. If that describes your phone behavior, you might want to look into a bottom-dollar prepaid option being offered by T-Mobile.

Cnet’s Danny Sullivan recently stumbled upon the $30/month unlimited web and text prepaid plan on the T-Mobile site. The company doesn’t exactly smack you across the face with it, but it is there at the bottom of this page.

Of course, there are limits to the desirability of this plan. It limits your monthly voice calls to 100 minutes, which may be too few for many people. And the “unlimited” data isn’t capped, but the speed is throttled after the user passes a monthly 5GB threshold. This would not be an issue for most users, but may be problematic for consumers who use their phones as a roving entertainment center.

Complicating matters a little bit, you can’t just click a button and sign up for the plan. You’ve got to either buy a new phone or order a T-Mobile prepaid SIM card, which will run you a one-time charge of $10.

Once you get the phone or the card, you’ll eventually find the $30 unlimited option listed as one of the pay-as-you-go options you can select from.

But then you see in T-Mobile pink, a note that says “New activations only” for this plan. So if you’re a current prepaid customer, you can’t go changing your current plan with the click of a button. But what about existing T-Mobile customers who are out of contract — would they count as new activations or are they considered existing accounts?

Sullivan didn’t have an answer for that, so we asked a rep for T-Mobile and got what appears to be decent news in reply:

“If you are a T-Mobile postpaid subscriber who is out of contract (or any other obligation) and want to switch to this $30 plan, you can do so through T-Mobile.com. You must either purchase a prepaid device kit from Walmart or a SIM card from T-Mobile. However, you do not have to activate a new account; we would simply do a rate plan change on your existing account.”

Of course, this all comes with the caveat that, unless you bring a compatible phone over to this account, you’ll be paying full price for your device. And unlike T-Mobile’s new postpaid plans that allow customer to amortize the cost of a phone over the course of several months, the company’s prepaid plans do not allow for that option. Additionally, the prepaid plan devices currently sold by T-Mobile do not have LTE capability. Of course, T-Mobile is still pretty far behind on building out that network, so that may not even be an issue at this point.

Sullivan had a Nexus 4 that he could just slide a SIM card into and he says he’s getting exactly what he’d expected.

“I generally get more consistent high-speed coverage with either AT&T or Verizon,” he writes. “Still, the speed was fairly decent, impressing me even on a recent trip to far-flung Duluth, Minn.”

He also attempted to tether his laptop to the phone so that he could access the Internet remotely and says it worked just fine.

Regardless of whether the T-Mobile plan is a good fit for you, it’s a good reminder that you should occasionally review your monthly data, voice and text usage to see if you’re getting the most out of your plan or if you could be saving money by switching plans or providers.

Want more consumer news? Visit our parent organization, Consumer Reports, for the latest on scams, recalls, and other consumer issues.