On Saturday, August 26th at 12:01 am, you will not be able to dial without using the 717 area code.
911 calls can be dialed as they are now. 
Landlines and cell phones are all affected.
You do not need to dial a "1" first, just the area code. 
Calls dialed without the area code will hear a pre-recorded message.
If you text, you will also need to put in the area code.
Your current number will not change. 
You should look at the contacts in your phone to be sure they have the area code included.
All calls that were local before are still considered local even though you are dialing the area code.