I've been meaning to write about this for quite a while now, but now that I'm travelling to the U.S. next week, it's top of mind again. I use Roam Mobility when I travel to the U.S. it's a fraction of the price of what the Canadian wireless carriers charge for U.S. roaming talk, text and especially data. The best deal they offer for smartphone users is their $3.95 per day for unlimited talk and text within the U.S. and back to Canada, and it also includes 300 MB per day of 4G data. That's a great deal compared to what you would get from Bell, Telus or Rogers. The big three carriers in Canada keep lowering their roaming charges because of services like Roam Mobility, but they were so crazily overpriced before that they're still not competitive. I can think of more than one occasion where I spent more than $100 with my Canadian carrier for a handful of MB of data and a couple of text messages over a few days in the U.S., and I was being careful—I actually argued the gouging charges and got a credit, but still.
Roam has removed any mention of who their U.S. carrier partner is from their website, but I'm almost positive that it's T-Mobile. I know for a fact that it was T-Mobile as recently as December 2013, so that's a pretty safe bet. They say "4G" speeds, so that basically means HSPA+ speeds of up to 21 Mbps. It's not LTE, but it's pretty damn good for the price.
Anyway, you can either buy a cheap device from them or buy a SIM card to use in an unlocked phone. I use one of their SIM's in my unlocked iPhone 5S and it works awesome. They've got lots of retailers in Canada that sell their SIM's and the news just came out today that they're now selling their products at Staples locations in Canada.
I don't need to explain it any further because they have a video below that does it for me. Happy connected travels!