I have managed to set mine up. I do have 1 issue, but otherwise it is there.
In setting up the Grandstream you 1st need to ensure you have your country settings. They are all different. If in the UK, I can help here. If not I am sorry, someone else will need to assist.
With regards to other settings. Suggest you first set up the Gatway in PSTN devices. That has a templete built in to the 3CX and is as simple as selecting it. The bulk is auto populated. - If you have done one, delete it and start again.
Then set up the Outbound Rules. I.e. dial 9 to get an outside line from extensions 100-150.. The route I.e. select from the list which Gateway (VoIP, Grandstream, etc) and then if any digits need stripping. In this case 1, the 9 for the outside line must go. Then if you have more than 1 phone line and you wish to control which is selected for the call you need to PREFIX (Prepend - crap language) 99 and then the line/channel. I.e. 1, 2, 3 or 4
So in this case if you set it to 991, it means that anyone calling from Extensions 100 to 150 and dials a 9 will get the Grandstream line 1 to make an outside call on PSTN... If this is not required because it does not matter which line they dial out on, leave blank.
Once that is done, go back into the Grandstream as you need to add the details to a Profile (normally 1) on the Grandstream and then the channels, selecting the appropriate profile.... I can send screen shots of this if you want... SOme of the Channel settings and all of the FXO settings are country specific.
