You are mostly right, i live in Venezuela, here we only get charged for data/outgoing sms/outgoing calls. Incoming sms and calls are free, as they should. Of course, our cell plans suck, for example i only get 60 minutes a month, 300 sms and 250 MB of data.
You are wrong about whatsapp not caring for new accounts, it is widely known whatsapp 450M users have about 70% of daily use.
Here a trick for whatsapp users: don't want to pay anually? Have android? Borrow an iphone, put your simcard, buy whatsapp for 1$, put your simcard back into your android phone. Boom, you get lifetime service for 1$.
Whatsapp is good enough, its strenght isn't security or privacy, but rather its comfort. You don't need to add anyone, no pins, usernames, passwords or logging in. If you want security then use BBM.