Traveling data hogs rejoice. Rebelfone has the best data rates yet for roaming SIM cards, and its voice and text rates are competitive with rivals like Maxroam and Telestial. If you're traveling to one of the 13 countries it covers, and you want to bring lots of data with you, it's an excellent choice.

Like other roaming SIMs, Rebelfone's rental SIM works with unlocked GSM phones. The card will work in AT&T and T-Mobile phones as long as they're world-compatible (and you ask your carrier to unlock your handset), as well as in Sprint's and Verizon's slim selection of "world phones." The card will fit in the iPhone 4S but not the iPhone 5, as Rebelfone offers full-sized and "micro" SIMs, but not yet the unique nanoSIM used by the iPhone 5.

Of course, you'll get the lowest rates of all by buying a prepaid SIM on the ground at your destination. But that isn't possible for a lot of travelers stymied by language barriers, confusing local rules, or just unfamiliarity with a city. Getting a SIM in advance also lets you tell your friends your new number before you leave.

We used Rebelfone in Spain with no complaints. The SIM came with a red instruction booklet with our phone number and PIN inked in the front. We popped the SIM into a Samsung Galaxy Nexus (MicroSIMs are also available for $5 extra) and the phone automatically set itself up with the right APN for data services. Online customer support is available 24/7 if you can't get the APN set up.

Since the SIM is actually a local SIM, you have a local phone number and there's no callback rigamarole—it's just straight dialing. I'd very strongly recommend monitoring both your voice and data usage, though as data overage is generally a dollar per megabyte. The free app Onavo Count can help with that.

Pricing and Plan

Rebelfone takes a unique approach: rather than selling you a prepaid SIM, it prefers to rent you a postpaid SIM. That gives it access to very low data rates, although you need to mail back the SIM at the end of your trip.

Rebelfone's best plans only apply to 13 countries scattered around the world: Australia, China, France, Germany, Hong Kong, Ireland, Italy, Singapore, Spain, Switzerland, Thailand, the UAE, and the UK. Texting and calling rates are variable and competitive; typically you'll get free incoming calls, with outgoing calls and texts costing from 20-40 cents per minute.

It's the data that really matters here. In those 13 countries, Rebelfone has "data packs" where you pay up front for giant data buckets, anywhere from 500MB to, in some cases, 5GB. In exchange for paying between $30-100 up front for your data, you get rates that competitors can't come anywhere near. Most other SIMs charge by the megabyte, and OneSimCard's 250MB EU data package, at $49, is considerably more expensive than these rates. That makes Rebelfone the best choice we've seen for travelers to these 13 countries who want to use large amounts of data.

If you're traveling to several countries within Europe, you can also get a pan-European voice or data SIM, although strangely, you can't get a SIM with both voice and data for multiple countries.

One of Rebelfone's other services is noteworthy: It offers very cheap rental phones, at 49 cents per day. The phones are simple flip-phones with no data access, but if you don't have your own world phone, calling rates are once again quite competitive here and this is a very good option. Rebelfone offers five rental devices: The Nokia C2-01, Blu Deejay, Unnecto Eco, Samsung GT3600, and Samsung C3050. They're all older, basic phones, but I'd go with the Nokia C2-01, as it has the nicest screen and camera.

If you don't want your friends to have to call a foreign number, you can rent a U.S. number for $2/month plus $0.49/minute for incoming calls.

As with all of these roaming solutions, Rebelfone makes it very difficult to figure out what the overall cost of your trip will be. You have to factor in the cost of the SIM (free to about $20), expected usage, any data bundles or prepaid credit you buy in advance, and $25 for round-trip shipping.

With, say, 20 minutes of outgoing local calls, 100 text messages, and a 500MB data bundle, a weeklong trip to Italy would cost you about $91. On a competitor like Maxroam, the same total price would only get you about 100MB of data, although you'd be able to take the Maxroam SIM to multiple countries (which you can't do with Rebelfone's single-country voice-and-data SIMs.)

Conclusions

There's no one best SIM for every trip. For single-country trips, the best choice is often a local SIM purchased in that country, but that may be too difficult for tourists. For heavy data users heading to one of the 13 countries listed above, Rebelfone's data packs are an unbeatable deal. Heavy data users should also consider XCom Global's International MiFi Hotspot, which offers unlimited data in some countries. That device can connect not only your phone, but also your tablets and PCs. Here at PCMag, we take one to every overseas trade show.

On the other hand, if you're roaming across borders but not using much data, OneSimCard has free incoming calls in 150 countries (as opposed to Rebelfone's 75 countries) with lower per-megabyte data rates than competitors. Outside of Europe, Telestial's regional Passport SIMs give you free incoming calls in a few countries OneSimCard doesn't cover, such as Bolivia, Honduras, and Iran, although data rates are pretty hideous.

I've stopped handing out Editor's Choice awards to these SIM cards because they're all the best for specific kinds of trips. If you've been frustrated with the data options for your next trip to its 13 key countries with data packs, Rebelfone's SIM will solve your problem.