I used to get lot of Google hits on Mobitel 3g / GPRS internet settings , I even did the same type of user level search on many search engines and and went trough site content and found most of them end up no where when they try to find proper GPRS settings. as per my knowledge I will list down common APN GPRS gateways used by Sri Lankan mobile operators.
Mobitel GPRS / EDGE /HSPA Settings
APN/Gateway : mobitel
APN name for a Prepaid Data Package : ppwap
APN name for a Postpaid Data Package : Dialogbb
Etisalat Sri lanka
GPRS / 3G / HSPA Configuration settings
APN : wap / web : Applicable for Pre paid
wap / internet : Applicable for Post paid
Airtel Sri lanka
GPRS / EDGE / 3G / HSPA settings
APN : airtellive / airteldata
Hutch Sri lanka
GPRS / 3G / HSPA Settings
APN : htweb
Most of the use packet data and open authentication.
*please note above information is not from official sources and it may change by the operator.
use them at your own risk