Do people who have my number see if I install WhatsApp If I install WhatsApp on my iphone, will other other people, who have my number in their address book, see that I installed it?
And if yes, is there a way to prevent that from happening?
Afaik everyone with your mobile number and WhatsApp installed can see if you are using WhatsApp, too. I don't know about a way to prevent that from happening, it's the only way to 'find' each other on WhatsApp and to start a chat.