Skype has revealed to some customers that the London telephone number they use for incoming calls will stop working next month.

Some numbers starting with "0207", the prefix for central London, will stop working on 20 December, Skype wrote in an email to customers.

"We're very sorry to tell you that we have to change your SkypeIn number", the email said. "As some of you may know, we get SkypeIn numbers from a variety of telecoms suppliers. Unfortunately, we have to return some of the 0207 SkypeIn numbers to one of our suppliers of London numbers."

SkypeIn numbers are sold by Skype to let users get calls on their computer from ordinary landlines or mobiles.

The central London Skype numbers affected are in the range from 0207870 to 0207871.

Skype is offering those affected a new SkypeIn number for free with voicemail for 12 months, although it's unlikely 0207 numbers will be available.

Some professional users have expressed anger over the changes, pointing out that for example, business cards and such like will need to be re-printed.

This will be seen as another blow to Skype's appeal to the business market following their black-out earlier in the year and recent virus warnings.