A PDA is not a Siddur:

It's easy to download hebrew prayers onto a PDA, and very handy to have your own electronic prayer book when you're at, say, a wedding. I often use my PDA as a siddur in my usual shul also, because carrying any load for a while, even a thick prayer book is hard on my back. The PDA's much lighter and easier for me to hold.

At Mincha for the last Fast of Tevet, a brief moment forced me to realize how much a PDA differs from a real Siddur: We were of course not wearing tallits, and the Torah was being returned to the ark. as the Torah passed us in the front of the room, people reached out their prayer books to touch it. Would I ever reach out my PDA to touch the Torah? NOT ON YOUR LIFE!