Balsamiq - I love it - the fonts and stuff can seem a bit cheesy - but I’ve take to this like a duck to water. Its much more useful than powerpoint, visio or other tools as its designed for wireframing.
Being built on Adobe Air means anyone can use it.
It’s very quick to create a UE design and while I couldn’t find a template or mockup for cell phone / mobile phone. I now made my own.
You can get my balsamiq mock fone hereTags:
Read more from my blog for an introduction and quick tips on developing in Hugo or UCTD.