By the way, Yahoo Mail push works. But it is sporadic at best. It took longer than 30 minutes for it to push an email. Not reliable if you want IM+ or Beejive push to your iPhone. MobileMe is still better but I don't plan to pay hehehe....
Beejive or IM+ 's push feature is actually to keep your IM accounts active in the server. Any incoming messages will be intercepted by Beejive/IM+ and then forwarded to an email account of your choice. I am not sure if there should be a 'number' tagged on the IM icon on your iPhone. But you will receive an email with that incoming messages appended. Then you have the option to reply it. Meaning to say, when you're off the net Beejive/IM+ will continue to be your middle man, handling and relaying messages for you.

Push notifications... not sure about it hehehe... guess not now for IM+ at least.

@feizaiII & davidmak,
Push notification is available on BeeJiveIM.

@davidmak,
You're right about YM push - it doesn't work all the time just as and when.  Also, I believe if the chat screen is closed on the other side, U won't be able to send a reply via email.

@rx330,
Assuming 2 messages are received simultaneously, the 1st message gets pushed before the 2nd but it comes back to back hence U won't be able to even read the 1st message cause it'll be overriden by the 2nd message

@feizaiII,
In Settings make sure you OFF push email notification.  And under Notifications, make sure U enable push notification from BeejiveIM.

@feizaiII,
I'm not too sure what the requirements are; perhaps U could read it up at BeeJiveIM's website.  I'm on an unlocked, unjail-broken iPhone 3G

This problem is not about being a 2G phone! It should occur on all phones without proper activation.
This problem should occur with all non-officially activated iPhones.
Apple Push Notification deamon (apsd) checks for valid activation records on the phone, ie. if you haven’t activated your iPhone through iTunes and your carrier, Push Notifications will NOT work.