Thames Valley Police is giving officers access to the Police National Computer (PNC), e-mail and other systems using XDA2 and M1000 handheld computers.
Using the devices, officers are able to reduce the time taken to perform a check on the PNC from three minutes to about 30 seconds for a vehicle and 40 seconds on a name check.
A pilot conducted with 70 officers in March is now being expanded to 350 officers for a further six-month trial.
Project leader Keith Gough said, "The next stage of the trial will see officers across Oxford using the PDAs and we will be closely monitoring their performance to ensure that an increased service is being provided."
Police officers are provided with either an XDA2 from O2 or an M1000 from Orange to access a range of police systems, including the PNC databases of people and vehicles, and also the electoral register to enable them to carry out checks in the field.
The software used was developed in partnership with Microsoft, which had a software developer based at Thames Valley Police headquarters working with officers and project leaders.
Thames Valley Police has also signed a £10m, five-year contract with communications integrator Affiniti to supply a managed communications infrastructure.
Through the contract Affiniti will provide Thames Valley Police with a one-hour response to its 14 main sites.