using cell data while roaming

I am going to Europe soon and have both a mobile phone on AT&T (U.S.) and a OneSim Card (https://www.onesimcard.com/). I was curious how much it would cost me to use data while roaming in Europe (i.e., to surf the net or access e-mail on my phone) so I did a comparison between the two. AT&T will allow you to use cell data while roaming internationally but the per KB or per MB rate is so astronomical as to make it unusable. Instead they offer prepaid monthly global data plans that allow you to use data while roaming at a discounted rate, up to a data limit. OneSim Card on the other hand does not offer any prepaid packages but instead offers a lower per KB rate than AT&T. Here are the results:

OneSim Card
$0.01 / 10 KB = 0.001$/KB = $1.000 /MB

AT&T (standard internation roaming)
$0.0195 / KB = $19.968 /MB

AT&T (50 MB Data Global Add-On Plan)
$24.99 / 50 MB = $0.500 /MB

AT&T (125 MB Data Global Add-On Plan)
$49.99 / 125 MB = $0.400 /MB

AT&T (275 MB Data Global Add-On Plan)
$99.99 / 275 MB = $0.364 /MB

AT&T (800 MB Data Global Add-On Plan)
$199.99 / 800 MB = $0.250 /MB

As I said, AT&T's standard roaming data rate is ridiculously expensive. OneSim Card's data rate is far cheaper but still not as cheaps as if you went with one of AT&T's Global Data plans. Depending on how long you're going to be away for, and how heavy a user you are will determine which one is best for you.

Awesome post! This is something that has always confused my while traveling - instead I always end up just skipping it and using free wifi instead, but it can be pretty inconvenient sometimes.

One of the other things I really need to get a better handle on is what networks and phones use what technologies, and where that can be used. For example, can an AT&T iPhone (irregardless of roaming or not) be used in Prague? Does it depend on what version of phone you're using? These are the things I wish there was a single resource to go to so you can find out.

I went to Puerto Rico just a few weeks ago, and I couldn't even figure out if I'd have extra charges using voice, text or data while there. I have a Verizon iPhone 5, and using their website they gave no real specifics on if it would be roaming or not. When I got there, it turned out the phone wouldn't even work there, so I didn't even have to worry about it.

Does that oneSim card work anywhere in the world at the same rate?

Thanks for reading!

I just got back from my trip to Amsterdam and here are a few things to add to my post, things I learned.

My iPhone had no problem working in Amsterdam, both on roaming data, roaming text, and roaming voice. I won't do the math here, but comparing my two SIM chips (the One Sim and my AT&T) on a voice calls, the One Sim is far, far cheaper. However, it was too inconvenient to carry around my iPhone for data and my second phone for voice and since I did not plan on making calls anyway, I just paid for an AT&T int'l roaming voice plan (for the one week I was gone), which wasn't too bad.

I had thought of only using data only when I was near wifi as well, however, with roaming data, i was able to use it anywhere and everywhere. By far the biggest advantage of this was being able to use the GPS/map feature. Looking for hotels and sights were a snap just buying clicking on the map and having it locate you in relation to everything else. It was difficult to actually get lost. Another cool thing was, while taking trains from city to city it was fun to follow along on the map/GPS to see where on the route you were. I paid $200 for the 800 MB plan, which is the biggest plan they offer and also quite expensive. In the 10 days I was there, I ended up only using 400MB.

A word of warning though, be very very aware of which apps use cell data and whether or not you've left them running in the background because that could be dangerous. I left the GPS running in the background a couple of times and ended up using 20-30MB of data in one short burst, which was scary. I was hoping to geotag all the photos I took on my iPhone, but that would have required location service to be running all the time on the camera, which would have used a lot of data, so I had to turn that off.