My wife (who might be in Europe twice this year and once next) would like to know:

1. Does each "area code" in Europe require its own SIM card, or could the same SIM card be used? For example, if she buys a card in Ireland (087) can it also be used in France?

2. If the answer to #1 is yes, how much more might the calls cost if made outside the "home area"?

3. She plans to buy an "unlocked" phone here and take it with her. Does this seem like a viable plan?

Thanks for your help!