Its so cute, isnt' it? My ds is 13 mos and that is one of his fav activities. He does it w/ the real phones, a toy phone, a old cordless phone that he has as a toy, the remote control...
He doesn't say hello or anything like it yet, but he has a disticnt "phone word", which sounds sort of like: aa-BA!
He also likes me to pretend to talk on the (real) phone. I find this somewhat ironic, since if I am *actually* talking on the phone, he screams and tries to pry it away from me, but then when I'm done, he *insists* that i pretend to talk. If I try to give it to him, or to say "bye-bye", he gets mad and shoves it back up against my ear
ahh, if only we could make sense of the whims and wants of a 13 m.o., huh?