Wirelessly posted

Youtube will play with OS4.5. If Opera won't work you can easily use the BlackBeryy browser.

As for IMs, I think it depends on I'm program -- some are data based (and may work on wifi), while others are text messaged based. In the case of the latter, you can still send IMs/text, it'll just be more expensive (you don't need a text plan in order to send and receive text).