Quote from the review at The Register:
“Dodgy keypad layout aside, the SX1 is never going to rival either the Treo 600 or the P900 for entering larger volumes of text than brief SMS messages. Siemens no doubt considers those phones as rivals, but they’re really battling it out with each other, leaving the SX1 head to head with the 6600. Both are phones that offer a good deal of PDA functionality – the Treo 600 and the S900 are coming at the problem from the other end, as PDAs that have been shaved down to work as mobile phones too.
Which approach best suits you with depend on how you use your phone. For me, it’s about voice communications and the ability to carry personal information around – my inbox is too full of spam for my phone to be a viable email platform yet. Out of the SX1 and the 6600, I prefer the former, despite being a long-time Nokia user. I could get used to the SX1’s unnecessarily annoying joystick and weird keypad layout – the 6600’s ‘wading through treacle’ speed, bulk and poorer battery life would be more difficult to acclimatise to.”