Yep, a lot of people trade in their Sidekicks. They also trade in their Blackberries, their Nokia, their Motorolas, etc...
They just can't make up their mind and sometimes think that they are cool if they keep up with modern phones... on the spot.
I know one guy who believed that if a new phone came out and people thought it was cool, he had to buy it. Even if his contract hadn't ended... he would break contract or spend a lot of money on a new phone so that he could use it.
It's not just Sidekick. I know a lot of people who had Blackberries and traded those in cuz they hated it and preferred Sidekick. Then there are those who hated Sidekicks and traded those in for other phones.
They just don't know what they want.
