Java platform: allows a phone to have third-party applications installed on it. This means functionality (such as the ability to conduct surveys) not originally built into the phone itself can be added, vastly improving the capabilities of the phone.
Millions of mobile phones and other devices support the Java platform.
GPRS: a mobile network technology which allows data to be transferred (as opposed to voice for example). Essentially, it is how a phone connects to the internet. It is a very low cost alternative as the field worker is only billed for the data transferred (which is minimal for a survey).
Newer technologies which provide faster transfer rates are becoming more common such as EDGE and 3G (used if available).