Finally, Microsoft has made it possible for companies to create custom Dial Plans. This is a highly requested feature as before it was not possible to change any normalization rule and to replicate the existing Dial Plan that an Organization has in place with their current Telephony System.
What are PSTN Calling dial plans?
By default the Service Country Dial Plan (This is the property on a user, you can find this in the Licenses assignment TAB for a specific user) will be applied to an Online User. If an Administrator has created a Tenant Global Dial plan this will be applied to all users except if a specific User Dial Plan is assigned to a user. This is the order and scopes of Dial Plans
The different with Skype for Business Server is that you create Office 365 Dial Plans with a new commandlet CsTenantDialPlan instead of just CsDialPlan
New-CsTenantDialPlan -Identity RedmondDialPlan -Description “Dial Plan for Redmond” -NormalizationRules <pslistmodifier> -ExternalAccessPrefix 9 -SimpleName “Dial-Plan-for-Redmond”
Create and manage dial plans in Skype for Business Online