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1) No
2) There are some thumb keyboards available for the X50:
Dell Axim X50v Thumb Keyboard
Home & Home Office: SnapNType Mini Keyboard for Dell Axim X50/ X51 Handhelds
(Be sure to read reviews on them before purchasing.)
3) Yes, but remember that you will need direct line of sight (unlike BT).
4) No, you can use IR keyboards or a thumb keyboard. There are also software keyboards that some people find quite efficient (e.g., Tengo).
5) If you search for reviews on virtual keyboards, you'll find many comments about how the lack of tactile feedback is a problem. But that may be a personal thing.