Posting on the walls of friends VK, FB, OK

Question

PHP

I came up with an idea for a promo site. Please tell me how things are in the following social networks: Vkontakte, Facebook, Odnoklassniki with the following functions:
- Posting content on the walls of friends: is it possible in each specified network and is the number of posts limited;
- Getting not only the user ID but also e-mail;
- With an already open social network, do you need to log in through the API or the entrance occurs automatically;
Thank you.

Answer 1

I asked myself, I’ll answer myself:
fb, vk: you can post on a friend’s wall, but 1 friend at a time
is ok: you can’t, if this is not an application, you can only post on your own wall.
The issue can be solved by writing a flash-application.

Answer 2

As for VK, everything is well described here: VK