Samsung Galaxy
I'm switching between carriers so frequently these days I'm not even sure what carrier I'm using right now. All phones in Iceland are open when you buy them (open meaning that you can choose whatever carrier you want) and I hope that won't change.
Yeah, it's total BS. In the U.S. they prevent you from doing that either by using different technology or different spectrum between carriers. Sprint and Verizon are CDMA networks, and T-Mobile, AT&T, and the rest are GSM networks. You can't just unlock your phone and switch between T-Mobile and AT&T because they use different frequencies for UMTS (HSPA and HSPA+ a.k.a "3G" and "4G" in T-Mobile's case).
I understand that Sprint and Verizon are pretty invested in their networks and aren't likely to change over to GSM or anything newer anytime soon, but the spectrum games are just blatant attempts to differentiate carriers by device. I wish someone would put an end to it.
One of the advantages of GSM is that your device isn't married to your carrier in any way, but they've managed to artificially remove that advantage to encourage customer loyalty and to tempt customers away from rival carriers by dangling sixy carrier-exclusive devices in front of them.