Originally written by Adam Wayland on Small Business
You do not say whether the business in question is a limited company or a sole trader or partnership. It makes a difference.
If the business is not a limited company only the business proportion can be claimed, so you will have to keep a record of business calls to justify a claim if the Revenue challenges your figures.
A typical solution for the sole trader wanting to claim mobile phone expenses is to take three to four months’ worth of bills, analyse the calls, and then work out the ratio of personal versus business related. You can then apply this ratio as a percentage of your phone bills for the rest of the year. You may find it useful to review the ratio on an annual basis.
If you are VAT registered, you need to include the VAT only on the business portion of your calls.
For Limited companies, everything depends on the type of mobile phone contract
If the mobile phone (or sim card) is registered in a company name, all the costs can be claimed. The main proviso is that ‘personal use’ must be ‘reasonable and not excessive’. The hardware (the phone itself) counts