You could try Flexiroam. You order a sticker that goes on your SIM card, which you apply at home and test it out. You can switch between your own SIM/carrier and Flexiroam whenever you like (requires rebooting the phone). Then it works in most of Europe and much of the rest of the world. $30 for 1GB, plus shipping for the sticker. The data is valid for 90 days, and you can buy more if you need it (including for a later trip, without having to install a new SIM card). It doesn't come with calling and texting (only data) but you can use an app like Talkatone to do those over the data or wifi connection.

I haven't used it in Europe yet, but there's a thread in the Travel Tech forum on FT, and people generally seem to be happy with it.