score:4
While Terminal 4 is not connected to the Skytrain system linking the other terminals, there is a free airside transit bus connecting it to Terminal 2. See details and map on the Changi site:
http://www.changiairport.com/en/transport/transfer-between-terminals.html
Update: So if I understand the situation correctly, you're starting your journey from Singapore? If you don't have checked bags, I would recommend checking in online, going through Immigration at T2, meeting your friend, and then continuing onto T4.