since I might have a Euro trip coming up soon and I realized that packed away in a drawer I had a great wifi access device - my no longer used previous cellphone! There's no chance of running up your minutes or using too much of your data since it won't work as a phone!
Ought to work -- do you still have a charger??
It may not be pleasant to use without SOME SIM card installed, even an expired SIM. I know my first Android kind of freaked out when I first turned it on without a SIM card - it gave me numerous "No SIM card" messages and slowed to a crawl, the point where I thought the phone might even be busted. But once I installed a SIM card, it behaved and became usable.
So - try it now without a SIM card and see how it works - or install some SIM card in it if you have one, perhaps not the one you use with your regular phone. (I have a pile of expired SIM cards purchased on past trips to Europe.)
Better yet, why not get the phone unlocked so you can buy a local SIM card to use it in Europe?
I have taken my Android (Verizon) with me on several trips to use on WiFi only, and it worked like a charm (no SIM).
Buy a used or reconditioned iPod touch. It's an iPhone without the phone.
I used to have problems with my Verizon Blackberry. In recent years I have taken Verizon iPhones and cell-enabled iPads. Some with cards but most without (Including iPhones)--acting as wifi-only devices--and they have all worked well. We have also used a Samsung Android tablet sans SIM and it was a champ and had a much better battery.