They're different shapes and styles too!
Traditional British phone boxes are indeed red and have lots of small panes of glass so you can see somebody standing in one all the way down to her feet - only the back wall where the phone is mounted is solid, the other three sides have the little panes of glass. You can still see the odd one here and there although most were replaced with "modern" silver framed ones with fewer, larger glass panes and even those are dying out in the age of the mobile phone. The SU! stamp is a good representation of a traditional British phone box.
A traditional British Police box is blue and is solid all the way round, the only way you'd see inside it at all is if the door is open in order to use the emergency phone (the window area at the top is too high to really see through). Not that Police boxes have been functional in the UK for many years (unless you count the Edinburgh ones that have become espresso kiosks but that's another story!).
The stamp Kristen linked to is a good Police box image and, as you can see, is completely different in shape and style than the phone box image. If you want to please a Whovian, invest in the Viva Las Vegas stamp!
(a Brit, lamenting the demise of the phone box as an icon on our streets!)
Last edited by Angelnorth; 01-02-2013 at 08:41 AM..