This is the third keyboard I've purchased, and it's the one most comfortable to use out of the packaging. The first two I purchased were the HP and Nokia BT keyboards, and this is the first one of the three that has worked perfectly with both PDA and smartphone.I'll focus on the aspects that mattered most to me, as most of the other reviews here already say what convinced me to buy this keyboard initially. So this is from my perspective, if you want more general reviews there are plenty of good ones, especially those labeled most useful:As you open this keyboard up, the "crease" of the keyboard is supported by a back panel, so the keyboard is held quite firm down the center. Also, packed up, this keyboard can fit into a large pocket, and can be carried around effortlessly. Finally, this is a 4 row keyboard (there is a 5 row version that I didn't know about) so all the numbers overlap the top row (qwert-) and a function (fn) key is needed to put in numbers, with numlock available, and a second function key for symbols. It takes some getting used to, but once you have the hang of the two function keys they are indispensable and used as often as shift is.With my other two keyboards, I had to "retrain" my hand positions along the keyboard to type "normally". That is, without accidentally hitting some of the oddly placed keys (shift, /, ', \, etc.) While this keyboard does not eliminate that problem, it does feel most closely to the layout and size of a full keyboard.Overall, it's a great keyboard, I can't comment on the battery life as I've had it for just over a month, and I haven't had to change the batteries yet. And I've been expecting them to day any day now at 15-32 hours/week use.If I had to change something I would: 1) Add a USB rechargeable built-in lithium battery. 2) Make the tray removable, as often I use the keyboard without the tray holding either phone or PDA. 3) Make the tray size changeable, currently, it can't hold my phone (Nokia E51) very stable, and not at all if I have the phone "portrait".In the design of the keyboard, once the keyboard is closed, the tray clasps onto the back of the keyboard. When open, the tray stays sticking out. It's really this issue, as well as my hopes of a rechargeable bt keyboard, that make me give this a four star. Really, though, it deserves a 5 or a 4.5.If you're looking for a BT keyboard and are constantly on the move or travelling, this is probably the best bet out there. I use it in my office at work, when traveling, in the car/subway, and anywhere else I have it with me that I have to wait for someone or something.I use it to send emails, text messages, browse the internet, make calendar appointments, for IM chatting, and writing notes. On both HP Ipaq Hx4700 and Nokia E51, but mostly on my phone.