Earlier quoted context omitted.
> you can talk to any of your friends if they install the app Yes, that's exactly the catch. Why should you require them to install anoter app if they might already use some other IM network? Approach of WhatsApp may be simplifies the initial registration step, but it adds to the global mess of the non interoperable IM networks. Negative impact way outweighs any potential comfort benefits, and authors who promote suc…
For most people it's far easier to just install an app instead of going through a whole setup and registration process and remembering a login handle and a password. I have a lot non-geek friends who are happy with how WhatsApp works. They mostly ignore all privacy issues with this.
One time configuration / registration is not really a burden. All users are familial with that process. And they don't do it each time they read their e-mail for example. As I said, the negative impact of non interoperability proliferation is way more significant.