handheld signature software

I want to be able to make a delivery to my customer and they sign the delivery note on drivers hand held phones - this is then sent directly back to office with times/date etc. We are only a small business and at most three people would use this - ideally I would like them to have a handheld device ie PDA or something similar - I want the system to be very simple - everything I have looked at has bells and whistles I just don't need !