Last year when I looked at wireless carrier's mobile plans, Sprint was the winner in this category for offering truly unlimited data, with no metering (or data tiers, no overage fees, and no throttling. Since then, T-Mobile has revamped its plans to be much more attractive than even Sprint's (whose plans are $79.99 a month for smartphones with 460 minutes for talk or $99.99 for unlimited everything). T-Mobile's unlimited everything plan is $70, including unlimited text, messaging, and data (no throttling or overages). You could also opt to just pay $50 a month for unlimited talk and messaging with 500MB of data or $60 a month for unlimited talk and messaging and 2GB of data. Even better, these plans include the mobile hotspot feature for tethering and sharing data over Wi-Fi with multiple devices...and there's no annual contract.
Best for: Heavy data users who download or upload a lot of files, stream videos on the go, or want to use their phones as modems for internet access on their laptops or tablets on the go.
MetroPCS offers very affordable no-contract plans, but only in specific metro areas (go outside those areas and roaming charges may apply). The cheapest unlimited talk, text, and data plan is only $40 a month, but it gives you 250MB of data that's then throttled after you reach that limit. The $50/month plan gives you a more generous 2.5GB a month of data (also throttled after you go over that amount) and unlimited talk and data.
An alternative to MetroPCS is Boost Mobile, with similar unlimited data (throttled at 2.5GB of data), starting at $50 a month or $55 a month for Android phones.
Best for: People looking for the cheapest "unlimited" plan who don't use a lot of data.
Virgin Mobile offers a great deal on wireless plans if you don't use a lot of talk minutes and are within the company's coverage areas: unlimited data and messaging with 300 talk minutes for $35 a month. The caveat is that the "unlimited" data is throttled to really slow 256 Kbps speeds after you use 2.5GB of data (or 3.5GB if you purchase the hotspot option which costs $15 a month). Also, most of Virgin Mobile's network is 3G rather than 4G. If you need more talk time, you can get 1200 minutes of talk for $45 a month or unlimited talk for $55 a month. The plans are all contract-free.
Best for: Those looking to save the most money on a wireless plan, who know they won't use more than 2.5GB data a month, and don't want to be locked into a contract. (Find out how much data you need)
If you don't need your smartphone for talking and only want mobile data on the go, T-Mobile offers monthly and prepaid data plans. You can buy a one week pass with no annual contract that gives you 300MB (enough for just basic email and text messaging) for $15. For $25 you can get 1.5GB of data for one month (there are higher monthly data passes, but they're not cost-effective).
T-Mobile also has a variety of other data plans including a $39.99/month 2GB monthly data-only plan and Micro SIM card plans. With the SIM card plan, you insert the card into your existing phone, rather than buying a new phone. The cheapest option for the SIM plan is 200MB of data and 500 minutes of talk for $39.99. Note that T-Mobile throttles data speeds to really slow 2G speeds after you use up 2GB of data.
Best for: People who only need data--and not too much of it.
What About the Other Providers?
Both Verizon and AT&T have stopped offering unlimited data plans for new customers. Verizon's single-line plans are an a la carte plans starting at $40/month for 450 voice minutes, plus $30/month for 2GB of data, and either pay-as-you-go text messaging (20 to 25 cents each) or $10-$20 a month for 1000 messages or unlimited messaging. Pretty pricey. The new shared Verizon plans may offer a better value if you have multiple devices.
AT&T's voice and text plans start at $39.99/month for 450 talk minutes plus $20 a month for 300MB of data or $30/month for 3GB, and $20/month if you want unlimited messaging. So, pretty much like Verizon's individual plans.
T-Mobile's bundled voice/text/data plans start at $69.99/month for 200MB of data and unlimited talk and text or $79.99 per month for unlimited data (throttled after 2GB) and unlimited messaging and voice. It's the better value of these three options, but still a bit higher than the ones above.