My family does an insane amount of international travel. At least one person has been living overseas everyday for over six months now, so we need to stay in touch. We've tried all of the astronomically-priced solutions from the big four carriers, and AT&T is on average the best of them, which is what we have, but we now want to try United Mobile of Liechtenstein. Since they don't sell phones and all of our AT&T phones are either iPhones or technologically insufficient, we need to buy one/some unlocked phone(s). We can also use it/them as spare phone(s), too. Our only requirements are for it to be at least triband GSM (900/1800/1900), UMTS 2100, and able to last several years. Any suggestions?