I have T-Mobile now... I think Sprint's option for WiMax is probably a better one. It's not LTE fast, but it's pretty snappy and I have a lot of options in terms of pricing.
Are you unhappy with T-Mobile's coverage? Because they have some really good deals if you go prepaid. Their coverage isn't the best but their data is excellent.
Just FYI, if you go with a Sprint MVNO there are a lot of disadvantages. The Sprint 3G network is incredibly slow, practically unusable it takes so long. I tested T-Mobile for about a week and it was super fast. T-Mobile's HSPA+ (~12 Mbps) was about 2x as fast as Sprint WiMax (~6 Mbps) and 40x as fast as Sprint 3G (~0.3 Mbps). Virgin Mobile is, I believe, the only one that has WiMax coverage, and only if you buy the Evo V. Which admittedly is a good phone and a decent value at $300, especially when you consider the plan is only $35 a month. For that low of a price, many people are willing to put up with slow data. And Sprint's actual coverage is good - you won't lose signal as much as with T-Mobile. But on Virgin Mobile, you can't roam onto Verizon either, you must have native Sprint coverage.
Straight Talk is a popular option. You have to be careful about your data use and don't use more than 100 MB a day or 2 GB a month. Other than that, minutes and messages are unlimited and you can bring your own phone. Costs $45 a month. You can use the AT&T network which has pretty good coverage.
And then there's also one called Page Plus. It's a Verizon MVNO. You bring your own device but it's a bit expensive with somewhat low data limits. Their best smartphone plan is $55/mo with a 2 GB monthly data cap and unlimited talk and text. Essentially the same as Page Plus but $10 more per month, but you get the Verizon network. The disadvantage is of course the cost as well as the speed - Verizon's 3G is much slower than AT&T's 3G, but still faster than Sprint. This is a better option, say, for someone who already has a Verizon smartphone out of contract and wants to save money, but it's not necessarily the best option if you want to go out and buy a Verizon phone for it.
Getting back to your original question, what's the catch with MVNOs? Usually the catch is there are a few perks offered by the big carriers that you don't get with MVNOs. Most MVNOs have either no roaming or very limited roaming. Virgin Mobile has none at all I know. Don't know about the rest but in general, you can't roam all the time like you can on a postpaid carrier. Then again, the postpaids are starting to crack down on roaming as well, at least data roaming, so that's not so big anymore. The big one I think is phone selection and pricing.
Postpaid carriers can offer the latest and greatest phones at low prices, making up the difference (and a whole lot more!) on monthly bills. Prepaid carriers sell phones without a contract, so you're getting older or low end devices at fairly high prices. No Sprint MVNO allows you to bring your own device either; you MUST buy a specifically branded device for that carrier. So you can't buy a Virgin Mobile phone and then activate it on Boost even though they are on the same network. That's pretty shitty IMO but that's how they do business. Straight Talk, T-Mobile, and Page Plus all do allow you to bring your own devices, but I know in Straight Talk's case that's a fairly recent thing.
And lastly, MVNOs tend to be less focused on smartphones. That's also changing but normally you won't get the same huge data allotments you get with postpaid carriers. Page Plus' $55 plan had a 1 GB cap until just recently when they raised it to 2 GB. Straight Talk boots you off if you use more than 2 GB a month. Virgin Mobile has a 2.5 GB cap. T-Mobile seems to be the only smartphone-centric one, offering a 100 minute, 5 GB plan for just $30/mo.
Facebook
Twitter