Thanks for your questions and asking for me.
Mobile Phone - Yes - establish how many free minutes are attributable to business and how many used in total, and then you can establish the % attributable to business. So say 240 minutes used, and 140 to business and 100 minutes private would be 140/240 = 58% and then apply the 58% to the monthly charge (and then add on any business calls that you had to pay for)
Landline - Do the same, check the itemised bill and establish the business calls made divided by total minutes, and then allow the element of business call costs and the % applied against the line rental for business.
Many thanks for your reply. That makes sense. However, these days most people do not get itemised bills (usually they have linked telephone, broadband & TV packages), so if there is no itemised bill are you saying that none is allowable.
Thanks for your follow up question
If you have one price all lumped in together for phone/internet/TV then you will need to estimate what part of that whole charge breaks down, to be attributable to each service. Usually the TV is the greater expense (if you have additional channels) so a bill of flat charge of £60 - I would attribute £30 to TV and £15 for internet and £15 for telephone as a start point, then look at the calls and landline fees.
But if you have no itemised bill for calls, then you can neither identify the costs of the business calls v free minutes/call charges, and nor can you identify the % attributable to business to apply against the landline fee, and the flat fee attributable to the telephone service. So can not really justify claiming anything, as you have no evidence to support the amount claimed.