MaxMind tests the accuracy of the GeoIP Databases on a
periodic basis. According to them, they are more accurate
for broadband IP addresses and less accurate for
mobile/cellular networks. Not being able to determine the
location of cellular networks is a general limitation of IP
geolocation services, due to the wide area cell phone
companies allocate IPs over.
They have compiled an accuracy chart available at
You also have the option to purchase their drop in database
which is more accurate then their free version.