Hel understanding the hiden app. Field Test App

Ok there is a number you can enter and it will run this app.
(Why this is imp. to me. To see if your phone or your service provider is messing with you.

First Screen is GSM Cell Environment.
Next is
PDP Contexts
GPRS Information
Network Information
Cell Information.

Im intrested in studying up about the GPRS Information and the Cell Information / Equvilent PLMNs and Service Cell/Mobile Country CODE. Which for me jumps between 404 and 65555
The 404 rings a bell because when my wifi fails it throws an error code 404

Some links that help in understanding the data in the feild test app would be nice.

Afaik it is kinda useless all over. Just seeing if the network is cipered is cool, as you see if someone is possibly wiretapping you with a IMSI Catcher.
Usally IMSI Catcher emulate a accesspoint or close cell tower. As they are not really part of the network their encrypthion is disabled by default othe rhan in a real network.
Well but as you are usalyl not afraid of IMSI catcher ... its useless .. mostly.