Many thanks to everyone who sent me replies to this query. Out of those who got back to me, the majority are using or planning to use iPads with 'satchels' or similar to carry them around in. One Library had tried a Galaxy tablet but found it a bit small; several others are using iPhones but one or two had found these too small. One was using the iPod touch with Facetime instead of using a phone. One other was keeping a low tech option using a 'runner' and two-way radios which worked well for them.
In terms of identifying roamers, most were using shirts of some sort - mostly polo shirts. A number sere using lanyards and/or badges and one equipped staff with sashes.
I think we will probably go down the iPad route - but if I do experiment with anything else which turns out to be any good I will let everyone know.
Library Customer Development Manager
University of West London