Up -Just kidding. May be call me up is used in the following context: When you are in a second or higher floor and say to somemoe in the first floor or in the parking lot to call you up (From there) in an hour, for example.

If Im not mistaken they mean the same thing. In the United kingdom I have heard them use the term call me up or ring me up...which means the same as call me in North America

I agree with Carly. I think 'call me up' is very slangy, only used by a small subset of the population. 'Call me' is more better grammatically.

I dont really hear the term "call me up" very often, the correct way to say it is "call me", I do hear "hit me up" in reference to talking to someone in slang