You are making this more complicated than it needs to be. I understand that you have a Patton FXO gateway that has two PSTN lines coming into it and that you have created within 3CX a trunk for each - presumably so that the Patton is not controlling inbound/outbound call handling in a collective manner. Each PSTN resides and operates independently from one another.
Additionally, you have a multi-account capable Fanvil phone and the desire is to be able to use the single phone and have the first trunk from the Patton ring on one account and then have the 2nd Patton trunk ring on a different phone account.
The auto provisioning is an issue given your statement about MACs. The 3CX templates are somewhat generic in their appearance in the 3CX provisioning tab. This is because there are simply too many phone makes, models and firmware versions which might require its own custom page. The fields you see in 3CX are the common ones and you will note that the accommodation for a second account on a given phone is not there for any make and model.
To get around the issue, you can either manually provision the phone as I will indicate below, or you can edit and customize the template and then save with a unique name (in case you need to add more X3 phones later that do not need this). I suggest that you factory reset the phone and Manually Provision using the phone web interface. PS - static and dhcp have nothing to do with it provided the phone is on the same local LAN as 3CX. The phone will apprise 3CX of its address upon registering. Of course, I personally prefer a reserved address or static rather than allowing the phone to be assigned a random IP. I also try and do this and then group the phones into sequential address ranges as it makes managing and possible QoS easier. Manually provisioning will give you a better feel for how the phone and system work and then, if desired, you can go back and see how it relates to modifying a template and do so if desired. Unless you understand the inner-workings first, trying to modify a template could be a problem.
So.....the phone has two (or more) accounts -
In 3CX you will create the 2 extensions of interest, say extension 100 and 200 (use whatever extension numbers you like that the system is set to use 2, 3, 4, or 5 digit) and once created, you will use the details in each to populate the above in SIP Line 1 and SIP Line 2 in the phone. I will assume 3 digit extensions and use the above settings as well as reference all system extension in the same 3 digit format. If you have set-up something different, you will then need to modify to your settings accordingly. I will mark the system extensions with a "^", so you know which ones you may need to change to meet your extension length.
Get into the phone web interface and go to VoIP where you will be able to select the desired lines - SIP 1 and SIP 2. The fields that show up are simply the fields used to establish an identity, tell the phone what is needed to get to 3CX and are used to register and authenticate with 3CX. They can be the same, or they can be different, but from a 3CX perspective they form extensions and in your case they will be the different extensions of 100 and 200. You need 5 pieces of info for each line - user ID (extension number) AuthID (as taken from the extension settings in 3CX), password (also from 3CX), the server IP/FQDN (3CX server) and the port which will be 5060 for BOTH LINES. Once into the phone, enter in the info for extension 100 in SIP line 1 and then enter extension 200's info into SIP line 2. In the Advanced SIP page for SIP line 1 scroll down until you see local port and enter in 5060 and then for SIP line 2 local port enter in 5062. On the same page, look for MWI number and input the voice mail extension number 999^ into the field for both lines. This will allow you to use the phone's button to access VM, but you will need to select the line key first so that when pressed, 3CX will know if the request is for extension 100 or 200. The phone will handle the RTP ranges as these can be found in the Network tab service ports. There you will see that the phone has a beginning port and then a range. Just leave these at the defaults.
Once both accounts have been established, applied or saved and made active, the phone should register to 3CX and both extensions (100 and 200) should be shown as up (registered) extensions. You should now be able to dial *777^ using either line key on the phone and see in the active call section of 3CX which extension is making the call. You should also be able to speak into the handset and get an echo of what you said. If so, the phone is functional.
Once the phone is up, get into the 3CX management console and go to SIP Trunks. Here you should see your Patton gateway trunks. Edit the first trunk and scroll down until you see "Route Call To" and then populate the fields with the extension 100 or 200, whichever is desired, for the desired conditions/options. Do the same for the Patton's 2nd trunk and route to the other extension.
Assuming you do indeed have the trunks set individually and that they are functional as such, and that the phone company is not doing any busy forwarding (rollover) on either telephone line, then when a call comes into trunk 1, it will ring the extension you set in the route for same, just as trunk 2 will do for the extension there.
You should then go to outbound rules and set extension 100 to use its trunk and then again do the same for extension 200. This will insure that on outbound calls, each extension will have the correct caller-id association as the phone company most likely controls this rather than 3CX (if in the US).
