I would post this issue on dslreports. They have a very active VOIP section and you can hear about all providers.

Viatalk is one of the few providers who cares about use abroad. I've used many providers abroad with no problem. Vonage is a good possibility because they include international calls to many EU destinations in their plan. Broadvoice offers some flexibility in voice usage, but there have been a number of complaints by people that Broadvoice places unfair usage restrictions on their international plans.

Another solution might be to port your number to TMobile. For $10 more a month, they have a plan called hotspot at home which gives you unlimited US calls when your phone is on a hotspot. The phone works fine from abroad.
That way, you have a phone for US visits and are free if you leave the phone at home in Europe. Just another suggestion. It also gives a phone with international roaming. When you relocate to a new country it is hard to qualify for international roaming.

Stu