Some providers may give you a DID number such as '011+33+144856535'. But if users are used to dialing '0+144856535' this is what you need to do:

• Login to the system administration
• Setup a trunk to your provider
• Setup a '01133144856535' DID
• Navigate to 'Settings->Servers->Edit->Other Networks'
• Set 'Mode'='Without access code'
• Click on 'Add Network'
• Set 'Prefix'='0'
• Select the 'Strip Prefix' option
• Set 'Hidden Prefix'='01133'
• Click on 'Save' 

Now users will be able to dial '0144856535' and the system will call '01133144856535'