"Americans who travel will also get ... notifications when roaming rates kick in."
That will be a boon for those live, work, or vacation on the southern shores of the Great Lakes (especially Lake Erie), where favourable atmospheric conditions combined with very calm waters at certain times in the summer (heat-wave-esque days with no wind) occasionally make some cell phones forget they're in the US, and cause them to latch onto a tower in Canada instead. (This has happened more than once to various friends of mine.)
International roaming charges, especially those garnered while your feet are still on your own home soil, suck big time...