I hope you are well and also hope you can help me!

We have Asterisk set up in a newly opened hotel. They have some very basic SIP phones for the Guest Bedrooms. Then for the staff, some nice Cisco 504's.
Anyway, they want to bar the guests from dialling internationally. I understand we need to amend the dialling plan (?) but i need this to only apply the Bedroom extensions.
Can anyone advise what i need to do?
Thank you so much!