Having to use a service that belongs to someone with no choice to use another service (you can email between gmail and yahoo but not between FB and Myspace for ex) as a communications “standard” is not a good thing
All of these services are proprietary and require that your recipient have the same software installed as you, or an account created on a particular service: except for email and SMS.
These two seem to remain the only two ‘open’ standards available for text based (and a little more than text via attachments and MMS) communications.
F*** using a service that your friends / family / contacts must use and/or install for you to contact them!
It’s still ridiculous that the WhatsApp client demands a phone number in any case, how is it useful to anybody? Just create an email based login like all other companies…