Using my BBM abroad

Hello,I have Blackberry Bold 9780 and I'm on contract.I am soon going abroad to Poland and I'm wondering how can I use my bbm without using roaming charges. I am planning to unlock my phone and buy Polish sim card and connect with any wireless network available ? Also what if I haven't done that would roaming charge me if I was outside and someone messaged me? Thank you.

If you keep your carrier's BIS plan, you will be able to use BBM, but will face roaming charges.

However, if you get a local Polish SIM and a BIS plan, you will not incur these charges.

I recommend the second option.