The Plumber will use different methods to unfreeze your pipes. Some of these methods include using a pipe thaw machine or a torch. Which are currently the most popular and widely used method by most plumbers.
You can also read how to unfreeze your pipes by yourself if you like, or ultimately if you can always call a licensed plumber.
Its always best to protect your pipes before they freeze with pipe insulation or heat tape. If they are in an area that is not heated you might want to heat that are with a portable heater or some kinds of heater other wise you could be in trouble.
The plumber can usually unfreeze your pipes pretty quick but that also depends on how much pipe is frozen as well as what kind of damage was done when they were frozen.
So keep in mind that after the plumber unfreezes the pipes you might also have damage to the pipes that will need to be repaired right away.