Unless you're looking at doing some extensive computing on the road, getting a smartphone with the option of tethering is probably more economical.
Speaking from experience working with (minion to an overlord
) ATT, if you add an aircard, often this will change your plan to a smartphone style plan.
If you're not as tech savvy and prefer to have a "regular phone," an aircard option might work. But if you want a smartphone, just make sure your phone can tether directly or make a wifi hotspot. Sparing use does not have a huge effect on your data usage, but be sure to monitor that closely to avoid overcharges.
As for the spotty service, do not rely on the maps of coverage areas that the retailer gives you. This is a vague reference. Even in areas that coverage is shown, often the coverage is not strong enough to do data signal. I would suggest using a range extender/booster. I've been very pleased with the Wilson line of products. These will even "add" coverage areas in some locations and allow cell usage beyond normal transmit/receive distances.
Good Luck!
