Business use of telephones
Always best to have dedicated telephone business landline but if not then you should reclaim business call costs (and you enter them on your P11D).
It is best to organise a contract for a mobile phone in the company name (one per worker). That way your company pays for personal as well as business calls, which is acceptable to HMRC. The same concession does apply to a device such as an iPhone or BlackBerry.
Note that for your company to pay, mobile phone contracts should be in the company’s name (if not you enter the amount you have claimed from your company on your P11D and look into changing mobile contracts).