Yes they are legit. I've been their client for over 8 years and have 104 domains registered with them. Good organization, and cheapest domain registration around.
I just got a call from that number and like you...No voicemail left...I too have a few urls listed with them...Strange they wouldn't leave a voice mail....Oh well...Have a Great Weekend! :)
I picked up & talked to the guy who called, who turned out to be a nice guy working as a telemarketer jockey. Seems that each of their worker bees has to make 200-300 calls a day, and there's no way for people to call them back, so that's why they don't leave msgs.
So I told him to tell his mgmt what a bad idea this was and that I had looked up the # on this website, which is a reporting site for troublesome mystery calls, and which is why I knew it was 1&1.
Also told him to tell his mgmt that calling people this way (repeated calls, no msgs left) was really bad for customer relations, company reputation, etc., etc.