It hasn't yet, but Nintendo's DS handheld is in a good position to catch up to the PlayStation 2 in terms of sales and dethrone Sony's venerable system as the best-selling console of all time. As of the end of March, the DS has sold 129 million units, hot on the heels of the PlayStation 2's 146.8 million units. According to The NPD Group's Anita Frazier (The NPD Group regularly releases video game sales figures), the DS should overtake the PlayStation 2 in "October or November of this year."
The PlayStation 2 first came out in 2000 and has a five year head start on the DS. Like Nintendo's handheld, it saw various iterations that made it smaller or cheaper, though it's now officially bowed out to the PlayStation 3, whereas the Nintendo DS is still in the running with a 3D version on the horizon.