serious question please help!

I know this has absolutely nothing at all to do with pregnancy or anything like that but I really need help!.. so, my husband has been getting calls on his phone but he has been at work when they call and he can't answer but they leave a message its like a machine voice saying he's getting sued for something... it doesn't say who they are calling for or what he's getting sued for or anything either.. my question is... if he was getting sued for something, can they even call you over the phone over it? I thought you had to be served in person...