We have several service engineers who work on various sites for a wide range of customers. At times we need to get additional data out to them and information back from them but at present they only have mobile phones. Has anyone any ideas on a suitable palmtop solution for data exchange in the field?

How much data?
In what format?
How much money have you?

In the 1990's I did a trial with the AA data system which they were happy with. It was limited to text of a certain number of characters, but when we tested it on the move, the errors really did kick in.
You need the bandwidth to provide fairly quick error correction and you will not be surprised to know that suitable frequencies will not be cheap, easily available or provide wide area reliable coverage.
The old Band I frequencies (about 50/60Mhz) should be available if you could put a proposal to OCOM, but the trials I did suggested that between antenna length and lack of power allowed meant a difficult engineering project. The RA (predecessor OFCOM) suggested I went back to them with suggestions - like more erp and bandwidth - to make the assignments workable, but I didn't bother.
I did find a manufacturer to produces equipment in that band and the equipment passed 'type appraisal' with flying colours, but problems in urban areas using that band coupled with sun-spot activity made it unreliable for mobile radio use generally.

Then they invented the mobile telephone....................................

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Norman