Once you know their IP address, you can find out an enormous amount of information from that. You can know:
- Their country
- Their city (roughly)
- Their ISP
- Whether they are dial-up or broadband
- Their Zip code
- Their telephone area code
The reason you can know all this information is because commercial companies have used trial and error to build enormous databases that cross reference IP addresses and all the above information. Of course, those companies want to get paid for their hard work of building those databases. Companies like: http://www.maxmind.com/app/products will sell you a license to lookup all the information you seek.
But there is no way to look this up in PHP without their database to cross reference.
