International Sim Card

I have a plan currently with T-Mobile Sidekick 3 and I for my going abroad during the summer in Europe. Should I take my phone and pay roaming charges? Buy an international SIM card here? Or wait and buy a stranger when I get there? I would also like to know if my plan currenlty active monthly would not be interrupted after my return from vacation and turned on my SIM card?
And does anyone know if I would be able to use the features on my side kick like AOL, Yim, MSM, e-mail and text, and if so how? thank you.

Yes, all.

If you are making calls, I suggest u get a new simcard with something like pay as you go and turn. the least expensive. ur using your current SIM cards will charge a lot of CPU for roaming. it wont affect your current monthly plan. a new SIM card should be about $ 20?? not that much.