Tomi Ahonen puts the number in context:
Now we have context. 800 million cars, 850 million personal computers, 1.3 B fixed landline phones, 1.4 billion credit cards, 1.5 billion TV sets. How many mobile phones in use today? In use today, yes, 2.7 billion (technically 2.7 billion in January, not December). They sold 950 million phones last year and the total worldwide mobile subscriber base grew from 2.1 billion to 2.7 billion. Three times as many mobile phones as automobiles or personal computers. About twice as many mobile phone owners as those of fixed landline phones or credit cards. And almost twice as many mobile phones in use as TV sets.
Phones are very aspirational. We project our personalities via the interchangeable covers, various decorations, stickers, and the massive industry of ringing tones. We customize our phone services further with ringback (waiting) tones, welcoming tones and background tones. Young people assign the same kinds of value to their emerging personality, their own perceived coolness etc, through their mobile phone, like older generations did with their first car.