I'm pretty sure you need to add a roaming package to your phone, or the sim won't find the network. That's certainly been the case with my UK orange phone, and then it has worked in both France and Spain.

With regards to top ups, you can do it online if it is a UK orange using the orange web site, and you can do it via online banking if it is a spanish orange assuming you have online banking. I can't help re US and French based phones though, but I guess the system is similar.