Primary line is with VZW on CDMA, but I've been using global phones due to travel and have it unlocked on GSM band - and my oversea prepaid GSM sim card roam and is usable on both AT&T and T-Mobile, with coverage extending to Canada & Mexico. I use an unlocked Sony W995 quadband phone that works on WiFi so I have access to old style mobile web browsing, plus a cheap T-Mobile prepaid (Gold) account that cost only $10 a year to maintain, pay as you go, 25 cents a minute - saved my tail a few times for emergencies when I forgot to take my phone. (After $100 cumulative or one-time refill, one earned Gold status (grandfathered in, I believe) A single refill of $10 every 365 days has kept it active, good for voice & text, mobile data is extra as add-on. SD card storage with enough MP3's to keep me occupied w/o draining the primary smartphone's battery for hours with a decent set of NC in-ear headset.

Worst case scenerio is that I lose the primary, Google Voice can ring my secondary T-Mo number (and/or call forward) until I switch & recover the main device, etc. Got 2 older HTC's smartphones that I can easily reactivate in case the main phone is destroyed or lost, until a replacement is done ...

When traveling away from home with Mrs. L, her identical phone is additional "backup" insurance - and we usually take a 3rd. phone with us, 4 extra oz. of weight that we can live with - thank godness for universal mini- and micro-usb charging on most Android devices. Another reason for using a Nexus 7 on the go vs. the iPad - fewer gadget accessories to take along.