I found this website . . . http://opensignal.com/networks/ . . . where they somehow test signals for cell and internet coverage around the world - country by country. You can get results showing each provider in each country. This may help decide which phone or stick you want in Mexico - or the US. As near as I can tell Verizon is the best in the US and Telcel is the best in Mexico - that is the best as far as how much area they cover - which is what matters to most travelers I think.
