We just went to UK, France, and Belgium last month. We have Verizon and they have a newer plan than when we went 2 years ago. With this plan, you are charged $10.00 per day per device that you want to use there. You are only charged the $10 per day for days you use the phone overseas. Your domestic plan covers your calls and texts while there, so as long as you don't go over your data allowance, you aren't charged. We used the phone, internet, and received texts daily and had no problems. To set it up, we just called them with the travel dates. It was no issue.
Also, just want to add that we found Wifi in almost every place we ate, visited, or toured. You just have to ask for the password.