Since the OP's nephew is going to be in Europe for several months, I'd just buy a different SIM card in every country. In France I've found Orange to be the best deal, and in Germany & the Netherlands I use T-Mobile (albeit a different T-Mobile SIM in each country).
The SIM is usually only about $20-30, which over a period of several weeks' worth of calls you'll easily save in cheaper calls.
Originally Posted by
BlindPilot
which sim card should I buy that will work in both Paris and Brussels?
Any mainstream French SIM card will work in Belgium, but you'll pay roaming fees. If you'll be making/receiving more than a few short calls in Brussels, buy a separate Belgian SIM card when you get there.
Originally Posted by
BlindPilot
How much for incoming calls from the U.S., or are they free?
Almost everywhere in the world apart from North America has free incoming calls as long as you're in the country where you bought the SIM.
Originally Posted by
BlindPilot
Can it send/receive text messages to/from USA? How much is the SMS charge?
All phones can send and receive text messages to anywhere in the world these days. Fees vary but usually anywhere from 15-50 cents a pop. Inbound texts should be free from anywhere in the world, like phone calls.