I am in the same situation. My wife went from a Curve to an iPhone. We tried Google Talk and there is not a separate app for the iPhone so that was out. We tried AIM and it worked well for a few days. I then found out that while it would say I was logged in on my Bold I really wasn't. She would send me a message and it was telling her I was not logged in. The 3rd attempt was Yahoo Messenger, which has worked great for the past 2-3 weeks. The smileys are a lot better on Yahoo, too.
OP, keep an eye on WhatsApp, actually is like the BBM for iPhones and it's working great, and the BB version is on Beta, once it finishes, they will make Chat available for iPhone-Blackberry.
Here's a novel idea...try speaking to them face to face...and if you can't for some odd reason try using the phone feature and call them.Really it works!!
Posted from my CrackBerry at wapforums.crackberry.com
I just email...don't have a txt plan, and really it seems kind of primitive with these 'smart phones.' (No offense to those of you txt'ers, just not for me)