Why do mobile messengers require phone number?

[Impulse_One]

[semi-rant mode on]

What's up with trend using phone number as registration credentials, especially on mobile platforms? (eg. mxit, whatsapp, bbm, telegram, etc) They have nothing to do with cellular providers at ALL.
Why not use email as regular messaging systems? (eg. skype, Oovoo, etc)

It is very annoying to expose one's mobile number to hell knows where, and even other's contacts in phone book.
In instance of Telegram it makes no sense, since its mission is to make communications secure and private, but logical fail! I would rather believe that ICQ/IRC/oldschool_IM has more privacy than above application.

I would be happy, if services were less restrictive in terms of registration. I understand it's easier to get prepaid sim card, a minor setback, but still inconvenience.

 

[Ho3n3r]

[semi-rant mode on]

What's up with trend using phone number as registration credentials, especially on mobile platforms? (eg. mxit, whatsapp, bbm, telegram, etc) They have nothing to do with cellular providers at ALL.
Why not use email as regular messaging systems? (eg. skype, Oovoo, etc)

It is very annoying to expose one's mobile number to hell knows where, and even other's contacts in phone book.
In instance of Telegram it makes no sense, since its mission is to make communications secure and private, but logical fail! I would rather believe that ICQ/IRC/oldschool_IM has more privacy than above application.

I would be happy, if services were less restrictive in terms of registration. I understand it's easier to get prepaid sim card, a minor setback, but still inconvenience.

Because you can add other people on Whatsapp via their phone numbers. This won't be possible if they weren't linked. Kinda obvious, I'd have thought.

BBM, well, I see it as a pointless product for non-BB users anyway, but have no idea whether you even link your phone number there, as you use a pin anyway.