What's so special about BBM? I never used so I got no idea how it is different from WhatsApp. Anybody wanna explain lilbit? ))
BBM is a completely different system compared to WhatsApp. While the later one uses your phone's contacts through their phone numbers, BBM uses a PIN I'd system, maybe a bit comparable to IM classics like ICQ or AIM. WhatsApp uploads all your stored contacts to their servers, while BBM doesn't. That means WA is more convenient at first, you install it, launch it and all your contacts are already there.
On BBM you need to invite / get invited users and add them by hand. Less convenient yet more secure, since 1st. you don't give away your phone number and share you PIN instead 2nd. you decide who can see and chat with or even exists in your contact list. After all BBM is much more private, but requires more work to set it up.
Also BBM has actual working sent/read indicators, WA only show when the message is delivered to WA servers and delivered to phone. BBM shows delivery to phone followed by and actual "has read the message" indicator. It also doesn't always show the last seen online times, which is something I really dislike about WhatsApp.
Last but not least BBM lately integrated their own, lets call it micro logging system named BBM Channels. Everybody can create their own channel(s), you are allowed to post a single picture and a text of up to 400 characters per post.
You can also limit access to your channel, either make it open or only let your contacts see it.
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