"אמא, מה נשמע?"
Translation:Mom, how are you?
The literal translation for "מה שלומך" would be "what is your situation/condition" or simply "how are you feeling" and for "מה נשמע" it's actually "what is heard".
There is no actual difference between the two, and I guess that like in every languages we have a lot of ways to say what's up.
Some more examples: מה קורה, מה המצב, מה הולך, מה חדש, איך אתה מרגיש etc..