Welcome to the free hamradio callbook. This callbook provides all data for free and you will not have to log in to see any detail unlike other sites. It includes also XML access for logging programs. You can use everything from HamQTH as often as you want without limits. The server has lots of power available and the Internet connection is unlimited.
Are you an application developer? HamQTH provides very powerfull API, it doesn't have any limits, you can query the callsign database and all other HamQTH features as much as you need.