Making outbound call, inbound caller on the line

http://en.wikipedia.org/wiki/Ground_start
"Local telephone companies typically provide two types of dial tone switched trunks -- ground start and loop start. PBXs work best on ground start trunks because those trunks can give them an on hook signal allowing for timely clearing. Many will work -- albeit intermittently -- on both types.

Normal single line phones and key systems typically work on loop start lines. The issue with loop start lines is that the PBX and central office can seize the line simultaneously; since neither gets the response it is expecting, the call is not initiated. The resulting condition is called glare or also known as Call collision.

In an idle circuit, the central office supplies -48V (nominally) on the Ring side and open on the Tip. A ground start PBX initiates an outgoing trunk seizure on an idle circuit by connecting of the Ring lead to ground (maximum local resistance of 550 ohms). The central office senses this condition and grounds the Tip lead. When the PBX senses this, it goes off hook, then removes the ground on Ring. The central office sends dial tone and the rest of the call proceeds normally.

In ground start signaling, the central office initiates a call by grounding Tip and putting the ringing signal on the line. The PBX has 100ms to sense this condition. The PBX goes off hook; if it had been trying to seize the line by grounding Ring, it releases Ring from ground and the call proceeds normally.

At the end of either an incoming or outgoing call, the PBX initiates disconnect by going on hook, or the central office initiates disconnect by opening Tip. When the other end detects the loss of loop current, it also goes on hook and the call is clears normally."

1) order ground start trunks from phone company
2) reconfigure analog card to work with 1

Another practice is to select out going calls from the last trunk to ring in and the in bound calls only meet the out bound calls when the last trunk is used. This is not as good as ground start.

Stanley

In the states you can't get Ground Start trunks anymore. I also am not aware of any DAHDI/Zaptel cards with ground start detect