From : http://www.gsmarena.com/iphone_os_4_...-news-1556.php

While Apple are still mum when it comes to the launch date of the next-gen iPhone, surprisingly, they have just announced when is coming the next iPhone OS. The iPhone OS 4 will be unveiled in a couple of days, on 8 April. And, reportedly, it will finally bring video calls to the iPhone.

Apple have sent out invitations for an iPhone OS 4 event that will take place on 8 April. The message itself welcomes the press to "get a sneak peek into the future of iPhone OS".
Slowly but surely they are catching up to the big boys. Watch out Nokia, here comes a phone to rival the video call abilities of the 6630 (released in 2004).