Sampling applications are quite common on all platforms these days. Of course there are a wide variety of applications available but few will do all the things you want in one place.
First off there are lots of voice recording applications. There's nothing wrong with these apps, but of course they do very little in terms of sampling.
On the Palm side there are only a small number of actual audio editing applications. My favourite is Wave Edit Pro, and of course the enterprise edition of the same app.
Wave Edit Pro is an excellent recorder and editor. It offers no plug ins or effects, but is very good at cutting and pasting sample data directly on a Palm device. Also, it has one benefit over other applications in that you can paste sample data from one sample into another.
Aside from Wave Edit Pro the best application for sample editing and manipulation is Bhajis Loops. Of course there's plenty of information on this blog about Bhajis Loops and on the chocopoolp site too.
However, the notable information in terms of sample editing is that you can do almost anything using Bhajis loops when it come to samples.
In terms of windows mobile applications, again there are lots and lots of audio recorders available, but fewer sample editors. There is one application like Wave Edit Pro called Pocket Mixer, which I have never tried personally but looks really good.. There are of course lots of applications that work with sample data:
4Pockets make the awsome MeTeoR (Multi-Track Recorder) application, which is one of the best audio applications for PDAs anywhere. 4Pockets also make the AudioBox Micro Composer, which has an onboard sampler.
Griff too has a sampler, as does Syntrax, although Syntrax has really amazing sample manipulation features. Mixx Mobile is also worth a look at.
Syntrax is available for Symbian devices as well as PocketPC, but aside from that I know very little