Or only just works?
I can do the majority of work from my mobile, exchange sync for email calendar and contacts etc. Works really well with a bluetooth headset so I can talk to customers, suppliers or engineers while I'm under a desk or getting dirty fixing a copier etc.
The problem comes when you need to view some complex information related to a call you are on or need to make. Eg you can't remember a 10 digit serial number, customer name, phone number etc to log a service call with a support provider. My solution is to have printouts in my 'manbag' (that I absolutely hate btw), laptop case or toolbox. It's a right pain in the arse keeping it all up to date, searching through it etc. What takes 30 seconds in front of a proper pc and phone sometime takes 10 minutes when out of the office or gets left for several hours until I can get back in front of a pc.
Ok if you can't avoid it or palm off work to other staff but a pain in the backside compared to a proper pc*.
* I say PC but you can probably do it with a mac if you want to look swish.