Before suggesting alternative IM's, I'd suggest to familiarize yourself with BBM's features first. There's a reason that people are asking for the BBM specifically. (prediction: rather than read up about BBM on their own, people will just (rudely) ask and challenge by saying things like "What's so great about BBM anyway?!?! Proof it!!!")
1) Ability to post picture 2) Fellow contacts can now see what you are listening to. (If option is checked) 3) Back up BBM Contacts 4) Longer Personal messages or away messages. (w/e you wana call it) 5) More smileys. (No offense but whats up with the Canadian Icon. LOL) 6) Send Files.. Pictures, Another bbm contact, Voice Notes, 7) Sync Avatars to Adress Book Entries. 8) Best of all.... Scanable Bar Code. Friend with a blackberry can just scan your barcode to add you as their contact..
Backup and restore The option to automatically save your contact list to your device or media card when your contact list changes is on by default. Chats You can do the following: View larger versions of pictures that you receive. Reply to voice notes by sending your own voice note. Clear draft messages from the chat field by pressing and holding the Shift key and the Delete key in an existing chat. Contact list screen You can change the spacing of your contact list to a one-line format. Also, the layout of menu items has been improved to be shorter and easier to navigate. Text messaging If you're using BlackBerry® Device Software 5.0 or later, you can change options so that you receive text messages in BlackBerry Messenger from BlackBerry Messenger contacts who are linked with a phone number in the Contacts application.