I don’t require your surname (aka: last name), however communicating with you will be much harder. I am not going to add people to my contacts if I don’t know the surname. It is that simple. If you aren’t OK with giving me your surname, that is fine – but I will not initiate communications since I don’t have your communications in my contacts because I don’t have your surname. I am not going to have 3 Joes in my contacts, and I have to figure out which Joe I need to reach while having a 67% of choosing the incorrect Joe. I will carry on a conversation via IM? as long as I have the IM. I will reply to emails, but will never write a new email to you. If you want me to be more active in communications, I will need your full name.