Is that means other user that already installed whatsapp will need to reinstall it again? Currently mine is working perfectly to chat between blackberry and android. What happen if upgrade to new version? Can we still chat with other devices too?

i never mentioned anything on commercial because i am more focusing in term of operational wise.
since WhatsApp is the most popular app that connecting between Apple, Android and Blackberry.
it is not worth at all if they change to new app but only usable for Apple.
Yes we can use other apps like viber, line or skype. but not every user in their Android and blackberry have that thing installed in their devices. some of them are lazy to create an account, such as Skype.
most of smartphone user go for WhatsApp because its easy to use, no additional account, no additional settings, no contact, its just plain taken from your phonebook.

No need to pay
Coz whatever u download is considered your purchased item already.

i have all, but i used none
coz my postpaid plan already got 100 sms free which i under-utilized