If you have AT&T now with no problems, have you considered Cricket Wireless? It uses AT&T towers. Have used it from Maine to FL with no problems. Don't know about international travel - have never done that and have no need/intention to. There is a Cricket business over in La Plaza Grande by Spanish Springs. Staff there was super when they graduated me from a flip phone to a smart phone last year!
Our Best Cell Phone Plans: Cheap, Prepaid Phone Plans - Cricket
$50/mo after Auto Pay credit
(Auto Pay credit not available with Group Save discounts or select promotional offers)
Cricket Unlimited 2 plan includes:
•Unlimited data access* with max speed 3Mbps
•Video streaming at SD quality (about 480p)
•Unlimited calls, texts and picture messages across the U.S.
•Unlimited texts from the U.S. to 38 countries
•Data access plus unlimited calls, texts and picture messages to and from Mexico, Canada and the U.S. (Min. 50% U.S. usage required.)
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Not sure if I have free time...or if I just forgot everything I was supposed to do!