I have an AT&T 958
This is a standard phone so I'm assuming you're using this in a home or small office, connected direct to a regular phone line, and that you're using calling services from your phone service provider. 3-way calling works as you describe: you press flash to get dialtone again, call the other party, then press flash again to connect the two so all three of you can talk. The point is that this is 3-way calling, not a forwarding or transfer function. You can't transfer a call to another number this way. Since you initiated the 3-way call, the connection requires you to be there; when you hang up the connection between the other two parties is broken.
Your line may also have call-forwarding, which lets you program a number that calls to your line will reach if you're away (an alternative to using voicemail or an answering machine and needing to check messages). But this doesn't allow you to transfer a current call to another number, only incoming calls.
The only way you can transfer a call is when you have the switching equipment (an office phone system, for example) at your location, and have at least two outside phone lines available. Then the system would allow your phone to disconnect, and still maintain the connection between the other parties. But both of the phone lines would remain tied up until the other parties hung up, and if you only had two lines you'd be unable to receive or make any other calls.
Residential customers with a single phone line don't have any option to transfer calls.
on Jun 08, 2011