There are so many mobile phones in use nowadays that it would be enough for half of our planet's population.
The first mobiles appered 26 years ago. According to the latest survey there are 3.3 billion phones in use worldwide today. Of course, it doesn't necessarily mean that every second person on Earth owns a mobile phone. The reason is that it is common to have two or even more devices per person in almost 60 countries while there are no phones at all in some parts of the globe.
People don't use their phones for-calls-only anymore. Also devices with Windows Mobile system are becoming increasingly popular.
When I'd visited Redmond campus (Microsoft headquaters) I was lucky enough to be introduced to the musician who composes ringtones for these mobiles. Benjamin Bethurum is one of the coolest and most energetic people I've ever met. You could've come across his music also on the Czech radio station - Radio 1 few months ago. Benjamin is going to release a new CD soon and it is going to compete also in one of the Czech hitparades.