If you are a startup, you are more than likely not to have an office. You are also very likely to have a Skype online phone number or Google Voice phone number. These virtual numbers are extemely easy to manage, forward to your mobile, etc. – all for just pennies. Everybody knows the benefits of global VoIP operators.
However, sometimes you need to register your company and the phone number for some useful services. For example, when you want to receive a code signing certificate, or register with a payment processing service, they would ask you to send a proof of your company identity (like Articles of Incorporation) and also a proof for your phone number – a phone bill to either your or your company. They used to demand a landline phone number, then they started accepting mobile numbers, and just recently they started accepting virtual phone numbers.
I was able to register with our Skype online phone number recently. Moreover, because Skype.com has so poor order/bill history management, I ended up simply sending screenshots of a few webpages with the Skype account details and payments. After some arguments they accepted that proof. Of course, they did call the number a couple of times. This exact trick didn’t work last year. So, it’s really cool that you can get by a virtual phone number, sending a virtual bill, and they are still happy.