As Alan said, why deal with getting an METV. Why not just come in on a 30 day stamp, if you want to stay longer, you can extend it at immigration for 30 days for 1900 baht. If you want to leave Thailand and come back, no problem. You get a fresh 30 day stamp when you re-enter and start process all over. For 3 months, this seems your best option.
Sprint and Verizon, At&T don't work here. Different frequency, or something like that. I keep my Tmobile phone active to receive texts needed for verifications to log in to online accounts. Also, as back up data service when I need it.
chiangmaivisarun.com I recommend. Nice, clean, ac van. The driver I had was great, fast but not crazy. I even gave him a decent tip cause I felt he earned it...tough drive with half the trip being major road construction...literally. Drop you off right at the border, wait one hour, then load back up and head back. Pick you up very close to your place and drop off. 990 baht.