Why is my typing in Yahoo online messenger delayed?

When I talk to my friends in Yahoo online messenger, the typing is delayed. It has only started to do this since I upgraded from classic mail and it ONLY does it in messenger. I send my messages to my friend's cell phone but I don't know if that's even significant. I've tried de-fragmenting my computer, I've tried running anti-virus scans, malware scans, and registry scans and I've tried restarting my computer. Nothing has worked, the typing in chat is still delayed. Please, help.