While spot may be preferred for the emergency signal (About the main benefit other than no data connection needed to upload pings).
BUT...
You can't beat free boyz! Yepper, Bubbler with tracking sent to spotwalla = $0.00 subscription fees.
On the data. I have Verizon and it works perfectly with Bubbler running in the background on my Samsung phone. I also use the phone as a BT connection to my Garmin (BMW Nav5) GPS, it gives me a weather overlay on my GPS screen (nice to see the clouds/storms and animated directions of, as you ride). When I go into Canada I simply put the phone in Airplane mode. I lose my weather overlay, I also now am buffering the pings up to spotwalla. No biggie other than for real time trackers. When I get to my hotel (I can wifi it to update) or I can wait till I'm back in the U.S. to trigger back out of Airplane mode.
For me, works perfect. No additional fees... mainly cuz I'm a cheap bass-tard and hate subscriptions!