Can I use apportionment for my phone bill?

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Im just wondering, as with the apportionment rule with private vehicle use, is is possible to use a similar method with a mobile phone bill.

Ie: I have a £20 per month line rental contract with 250 free minutes, however I often go over resulting in a higher bill. but lets say i keep a record of every bill, then a record of all "property related calls"
to keep the math simple, lets say I use 5000 minutes per year in total, with 1000 minutes used on property calls.
Could I then say the 1/5 of my annual phone bill is classed as an expense?

does anyone else do this? does it work?

Any advice is appreciated

Thank you