You're best bet is to buy a "pin line" off a website like sythe.org (Can I post links? \o_O/)
which allows you to get pins for free.
How it works is that the pin line is a phone number that some companies have to allow employees to use the business line when they're out of the office, so by calling this line you can then go on to use the companies line for all premium rate charges, avoiding the cost.
It works somewhat like a proxy for the phone :L
Of course it's illegal so I'm not advising you go and do it ^_^