WhatsApp - who sees the numbers that I have

[Kenshira]

Say I have whatsapp on my iphone and have a contact called contact 'X' in
my phonebook. Contact 'X also has whatsapp but doesn't have my phone number
in his phonebook. Once I install whatsapp on my phone, contact 'X will show
up on my list of favourites on whatsapp. Once he is added on my phone, am I
added on his phone automatically?

Basically, my question is, if two people have whatsapp but only one person
has the other persons number, what will happen?

If i have someone's number but they don't have mine, will i show up on
their whatsapp contact list?

Does it depend on the version of WhatsApp someone has or it depend on
which phone is or what?

 

[Blueshirt]

My understanding of how it works is; WhatsApp will look at the phone numbers of your contacts, then check with it's servers to see what numbers are already registered for the WhatsApp service. So that any WhatsApp user whose phone number is in your contacts list will automatically appear within the WhatsApp 'favourites' section on your phone. Obviously for the other person it works exactly the same. Which should mean that if somebody doesn't actually have your phone number in their list of contacts on their phone, then you shouldn't appear in their WhatsApp favourites section... as your phone number is not on their phone for it to be checked against the WhatsApp servers enabling it to be incorporated within that persons WhatsApp.