Is this the best smartphone plan ever?

T-Mobile has a great plan for those who use their smartphones primarily as data devices. But finding the plan can be a challenge.

Don't talk on your smartphone much, don't like the idea of a contract, and don't want to pay a lot of money per month yet still have plenty of data? T-Mobile has the plan for you, if you know where to find it.

For only $30 per month, T-Mobile has a plan that offers 5GB of 4G data, unlimited texts, and 100 minutes of talk time. It's the cheapest prepaid plan I've seen from any of the major U.S. carriers.

Verizon's pay-as-you-go plans start at $60 for only 500MB of data; $70 gets you to 2GB. AT&T's prepaid plan for smartphones is $65 per month for only 1GB of data. Sprint's pay-as-you-go plan is $70 for smartphones, with unlimited data

At half the price or less, and with 5GB being a pretty roomy data allowance, the T-Mobile plan is so good I'm almost afraid writing about it might make it disappear.

Finding the plan
You won't find the plan listed on T-Mobile's main site -- not that I could locate, when I went looking a few weeks ago after hearing about it. Even T-Mobile's "Bring Your Own Phone" page doesn't suggest there's a prepaid option lurking out there.

T-Mobile will shift you over to its prepaid site, if you do a search for that. The home page of that site gives the impression that plans begin at $50 per month for only 500MB of 4G data. However, if you go to the page listing all prepaid plans, then scroll down to the bottom, you discover the magical $30 option:

You can't order the plan initially. You have to either order a SIM card for your phone, which will cost $10, or buy a new phone (which will add the SIM card to your order).

After I placed my order, the SIM card arrived in about a week. I worried when reading through the activation instructions that the plan was no longer offered, as it wasn't listed:

But when I went through the activation process online, I was relieved to find the option was shown there, with a little "New activations only" notation that I'll get back to:

In short order, the Nexus 4 that I was using with the SIM card was up-and-running with T-Mobile. I've been using it with the service for about two weeks now.

Decent speed and coverage, for the price
What I've usually found to be the case with T-Mobile in the past has remained true. I generally get more consistent high-speed coverage with either AT&T or Verizon. I have phones with both of those carriers, as well.

Still, the speed was fairly decent, impressing me even on a recent trip to far-flung Duluth, Minn., where I flip-flopped between 3G and H on my phone (H presumably for either HSPA or HSPA+, but nothing I can find at T-Mobile's site explains this clearly, perhaps because of all the network changes going on).

Since the Nexus 4 isn't 4G LTE capable, I couldn't test out T-Mobile's fledgling coverage (seven cities, so far). I have tested the built-in tethering option on the Nexus 4 to share my connection with my laptop, and that worked fine. Heck, my editor-in-chief at Marketing Land, Matt McGee, who tipped me to the plan, has even been using it to power his testing of Google Glass.

As this is a backup phone for me, I'm not too worried about running out of either talk time or high-speed data. But even if it was my only phone, I've found in the past that 5GB of data is an ample allowance, and personally, it's rare for me to use many of my voice minutes at all.

Things to consider
Now back to that "new activations" caveat. If you're already on T-Mobile, that should mean that you can't switch to this plan from anything you're on now. It might also mean that if you activate a new line of service, T-Mobile might not let you port your old number to this new line. I can't confirm any of this, because I'm new to T-Mobile. But I would suggest that all things are possible if a carrier really wants to keep you. Talk to customer service if you're already at T-Mobile and really feel this is the plan you want.

If you're not at T-Mobile, you should be able to activate the new line, then port your phone number over to it from another carrier. Again, I can't confirm this, as it's a secondary phone that I use. I didn't try to port a number over to it. In fact, as a Google Voice user, I don't need to. I ported my main phone number to Google Voice long ago. People call that number, and it makes any of my phones ring. When I call out, only my Google Voice number shows.

I'm sure there are better smartphone plans out there for people with particular needs, such as wanting more data, needing a family plan, or wanting more talk time. But for the smartphone user looking for decent nationwide coverage in the U.S., support for many phones, and a low price, T-Mobile's got a super plan.