I have installed FreePBX 184.108.40.206 in my office. I want to configure one extension on more than one hard/soft phones. When I configure my extension on second hard/soft phone it stops working on first device. Anyone can guide.
Not really something you can do the way you describe is SIP.
There are other technologies where something like this is possible (DAHDI or Chan-SCCP-B Shared Lines).
The “correct”-ish solution is to set each phone up as different extensions (so they can be active at the same time) and the use them in a ring-group. When people want to send you a call, they send it to the ring group and it rings whichever phone(s) are active at that time. Putting people “on hold” won’t work between the extensions, and they are still completely separate lines (depending on setup, different voice mails, etc.)
If you want them to share “500” (for example) you can make the individual extensions “5001” and “5002” (or “501” and “502”). You can set up the caller ID, etc so that it all looks like you are calling from 500, but you’re the only one that needs to know the truth.
Using chan_pjsip with asterisk 13, you can do this by adjusting the ‘Max Contacts’ parameter in Advanced tab of the pjsip extension. Otherwise you have to use one of the a work-arounds such as suggested by Dave.