As smartphone clients are restricted in computational power and bandwidth, it is important to minimise the overhead of transmitted messages.  This paper identifies and studies methods that reduce the amount of data being transferred via wireless links between a web service client and a web service. Measurements were performed in a real environment based on a web service prototype providing public transport information for the city of Hamburg in Germany, using actual wireless links with a mobile smartphone device.  REST based web services using the data exchange formats JSON, XML and Fast Infoset were evaluated against the existing SOAP based web service.