I found this in a field in widcombe and tried (hard) to get Vodafone to let the owner know or to put me in touch with them but with no luck (how hard can that be Vodafone!?)
Apparently it is a GPS tracker for your pet (or anything really). It is locked to Vodafone so no use to me (or my dog ;) but maybe to someone.
I needs a new plastic holder and charging cable but i think both can be found online.
I have no idea if it works and no way to test it.