In reply to The Ice Doctor:
Interesting thread and I am going to expand on my first post.
As a few others have said, why wouldn't you want one of the most powerful tools in the box available.
My job would be very difficult without one.
I have hundreds of technical manuals on mine for the different machines I look after. (they would fill my van on paper)
A conversion app that I use to convert pressure and flow rates.
A calculator.
A database of the make, model, serial number, kW, spares needed and every job carried out for every machine I look after.
A camera
Email
Mobile Internet (useful for finding info on the odd machine I don't have a book for or as was the case yesterday I was in the field and needed to find a local supplier)
Google maps (sewage works are in spurious locations, once close you can often see them on Google maps)
Multi user calendar app, all my jobs and all my lads jobs and bookings available at the finger tips.
I'm sure I use it for other things too.
Personal life.
Internet access. (mainly forums)
Camera.
Imdb app
An app for a play station game I play.
Occasionally Google map's but if I'm not working I'm on my bike and getting lost on a bike is half the fun.
If I stopped working I would ditch the smart phone tomorrow and just have a small tablet to use at home and a compact camera in my pocket when out but from a work point of view, especially when you run the business from out in the field it's invaluable.
Yes before anyone says it businesses have run for years without smart phones but customer expectations have moved with the technology and if you can't react almost instantly they will move to someone who can.