Business mobiles - free calls
If you have a number of business mobiles within the same company it is possible to have a contract where all phone calls between these handsets are free. They do not come out of your inclusive minutes.
There are also contracts where it is free to call all 01, 02 and 03 landline numbers. Again this is outside of your monthly inclusive minutes.
By utilising these options it leaves your monthly inclusive minutes for calling mobile phones outside of your group. This is the most cost effective option as mobile-to-mobile calls are amongst the most expensive in terms of pence per minute.