The voice clips with the congratulations from each main character (to Rin) have been posted on the Free! official site! They’ll be up until the 8th of February 2014 at 6 p.m (Japan time).
Here’s what everyone says:
Nagisa: - Happy birthday, Rin-chan! Rin-Rin!
Rei: - Happy birthday. I heard from Nagisa-kun that your birthday is today.
Makoto: - Today’s your birthday, isn’t it? Happy birthday, Rin!
Haruka: - It’s been a while since I last congratulated you. I’ll only say it once. Happy birthday, Rin.
Rin: - Thank you. (said in English)
Check it out now!