Using Iphone 3g connection

For what? Your question would be completely ambiguous if you hadn't posted in the OS X forum.

You're talking about tethering. AT&T doesn't like it, but I believe there is a jailbroken app that lets you do it.

Don't let them "catch you".

There has been talk of a tethering plan, but I don't know what has become of it.

 

Please look at this thread:

http://forums.macrumors.com/showthread.php?t=599343&highlight=tethering

To understand the option that exists using Jailbreaking. Understand that we do not advocate this option and that, depending on your service provider, it may violate your terms of service and possibly subject you to some kind of retaliatory action (fine, termination of service, etc) from your provider.'

For more information about the possibility that AT&T and Apple will offer official tethering and/or that official tethering will appear elsewhere in the world, please look here:

http://forums.macrumors.com/showthread.php?t=595933&highlight=at&t+tethering+official+iphone

and here:

http://forums.macrumors.com/showthread.php?t=598401&highlight=at&t+tethering+official+iphone

For more information about the App Store - based solution that was briefly made available:

http://forums.macrumors.com/showthread.php?t=535737&highlight=official+tethering

Additionally you can forum search for "tethering" and find lots of other threads on the topic.

Cheers.