I think a sensible way to deal with this would be to treat it in a similar way to Equipment under 23 'Equipment purchased for work' with a reasonable calculation of the 'change in value' over the contract period, which appears to be what you are doing anyway.
There is often an issue with the cost of calls from phones (work related or personal) but it depends on what is paid for by the Contractor which should constitute Defined Cost.
There is often an issue with the cost of calls from phones (work related or personal) but it depends on what is paid for by the Contractor which should constitute Defined Cost.