Be aware that it is not 100% free. Once you exceed the data limit in the package then you would be on top up rates (or service cut off)

I have an unlimited data package so my European roaming is free. A friend of mines plan has a monthly data limit and when he exceeded that he was charged by his carrier.

Do they really need to have their phones on all the time? It is possible to get by using free wifi in coffee shops, museums and hotel etc. Remember the days when we went out and about without a phone!

Why not ask your own phone provider what they offer in terms of short term packages? The only other thing I can think of is Lebara but you;d need to check the package and the data limits included.