Sometimes a couple of words are enough but I have to admit, it only applies to the minority of the SMS, Twitter and e-mails I send from my mobile phone. While in the metro or another public place without a lot of space I use the keypad of my Nokia N95 and T9, but it's a concession to the situation. If there's any chance I can sit down and have some space, I prefer plan-B, which is typing that message or e-mail using my Nokia Bluetooth keyboard with 10 fingers.
I've had mine for several years now with various Nokia S60 phones and have done everything with it from writing SMS messages to reporting from the Mobile World Congress. Usually the keyboard is not cheap, costing well over $100. I am not sure why, but Amazon.com currently sells the SU8W for around $57! Amazing! If I hadn't already two I'd buy one right away before they increase the price again or run out of stock. So if you've hesitated before due to the price, now's your chance!
In case you wonder why I write such a straight forward product recommendation, the answer is simple: For me and for those who've bought one in the past due to my advice, the Bluetooth keyboard has been a game changer and one of the main reasons to stay with Nokia/S60 in the future.