Using Sage in a tablet.

edit

I believe you can use Sage in the "cell server" using an iPad, and also of course online at a full server like sagenb.org. There is also an iPhone app which I think is available in an iPad version, but that is mostly for once-off calculations.

Finally, salv.us is a new Sage service which is eventually going to be specifically adapted for distributed computation and use on mobile devices (among other platforms).