Extensions can't call each other


Are there any settings (inbound, outbound etc.) or anywhere else that could keep the extensions in network from calling each other. most everything else works. I have a Grandstream ucm6204 PBX, 2 analog phone lines (copper) and a few Grandstream 1760 and 1780 phones and a Panasonic wireless Hub and 4 wireless phones. all hooked up to the same cat5e network . all network connections are 1gig except the 1760 phones and wireless hub. all switches and router are 1 gig. found corrupted phone log files and deleted them. upgraded bios from 1.0.18 to’t help . extension permission are all the same and outbound rules has same permissions. could it be some kind of nat setting? It was all working before with same hardware. restored from older backup, that did not change anything. Just wondering if some hidden setting could have changed to no let phones talk to themselves. If anyone has any ideas please let me know. I put in a ticket with grandstream but its been over 24 hours and not a work. I will be thankful for any suggestions . Does anyone know if there is a grandstream rep in St. Louis ,mo. please let me know. Thank you all. Pancho

P.S. all phones, pbx, and router all use static ips.


I know this is silly but you have got Line keys assigned to the phone for the registered account?

Without line keys you cannot make calls


a bad or missing dial-plan could stop it, but if it was working originally and nothing has been altered, then it is unlikely.

I would propose the question, what’s changed.
Most people say nothing until they figure out what changed.


format two phones, provision with Zero config and see if you can call between those 2 phones, and act accordingly.


I am not sure what you mean but I can call out on to outside people and we can get calls from outside. but just can’t dial other extension. if you do you get a busy signal and some error message like something failure to something I can’t remember right now but I will write it down Monday. Thanks for all the help.


not sure what a dial plan is . I will try to look that up and see if I can find the setting. Thanks for all the help. I will let you know what i find.


A dial plan establishes the permitted sequences of digits dialed on a device like a phone.

For example if you want to allow the phone to dial 3 digit numbers the dial plan would have a xxx in it to permit that.
If you wanted to dial two digit feature codes that start with a star the dial plan would have *xx in it.

Verify that the dial plan on the phones contain the digits that cover your extensions. If they have been changed or removed(usually by a provisioning file) it could inhibit local calls from working.


do you mean in the outbound routes on the ucm6204 . or do you mean on the phones themselves. I am using a grandstream GXP 1760 mostly and a few GXP 1780. How do I se the dialing plan on the phones. I can log into them with a gui and change but I don’t remember seing any dial plan set up I will look again. thanks for all the help. I’t sad that I can’t call Grandstream and talk to someone on the phone.


Best way to learn where a particular phone has a certain setting is to search the admin guide.

Alternatively you can open a ticket at helpdesk if you want to talk to Grandstream.

As a dialplan is in a different place on different versions of phones, I recommend the manual.
Traditionally it is found on the phones web interface in the accounts call settings in some fashion.


look like the default setting for dial plan for my phones. and outbound plan looks fine also.


All setting look fine but phones can’t seem to see each other. I can dial out .
I can get calls coming in.
When I dial extension like 29 it acts like it calling but I get a busy signal and the phone says No Response.
could there be a memory problem? could part of the internal hard drive be corrupted. Besides firmware update can you reload the gui and other programs on the unit. Does the reset reload everything. ? So many questions. If only there were someone I could talk to on the phone when I am sitting in front of the ucm6204 logged into it. Let me know your thoughts. Thanks. Grandstream won’t talk to anyone unless they are a reseller or one of there techs.


Given the expressed functionality, it does not appear to be a hardware issue as it would be off for the issue to only impact one aspect. As you can make and take outside call, this would tend to rule out the phones being at issue.

I think Damiano had the bets suggestion -

Take a couple of your existing extensions and phones-

  1. Delete the configuration of the phones from Zero Config.
  2. Delete the extensions of same from the system.
  3. Factory reset the two extensions
  4. Reboot the system.
  5. Re-create the same or create new extensions
  6. Using the same phones, re-provision to the new extension just (re-)created.
  7. See if you can then call between the two extensions
  8. See if you can call between the new and old extensions and vice versa.

We may need to see a network capture just to see exactly what is going on with the messaging as it is certainly odd that phone can get outside, but not reach one another. If the above does not work, please capture and post a call between two impacted phones.


I did all those things and they still won’t call any extensions.




I fixed it 4/11/19 evening. I did a factory reset, a few times, then loaded a backup from before the problems. Now things seem to be back to normal…I will know more after friday and see if it stays fixed. Thanks for all your help to everyone.