To strip items off of the number you will need to use a Java step.
Take the number and put it into a variable, then pull across the Execute Java Method and since the number is down in a string variable you will have that as a variable type here. When you go to the second tab "Explore Class information" Pick the following method "public String substring(int,int)"
This will give you 2 arguments, the first should be 0 the second will be 3. This will give you the first 3 numbers wich are the area code.
Regards,
Javier