Ok, thanks for your helpful diagnostics :-)
So, without a SIM card inserted, the PPP logs:
Apr 17 16:18:09 pfSense ppp[57660]: [wan] Bundle: Interface ng0 created
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] Link: OPEN event
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] LCP: Open event
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] LCP: state change Initial --> Starting
...
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] CHAP: Using authname "user"
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] CHAP: sending RESPONSE #1 len: 25
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] CHAP: rec'd SUCCESS #1 len: 4
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] LCP: authorization successful
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] Link: Matched action 'bundle "wan" ""'
Apr 17 16:18:09 pfSense ppp[57660]: [wan_link0] Link: Join bundle "wan"
Apr 17 16:18:09 pfSense ppp[57660]: [wan] Bundle: Status update: up 1 link, total bandwidth 150000000 bps
...
Apr 17 16:18:09 pfSense ppp[57660]: [wan] IPCP: SendConfigReq #1
...
Apr 17 16:18:28 pfSense ppp[57660]: [wan] IPV6CP: SendConfigReq #10
...
Apr 17 16:18:36 pfSense ppp[57660]: fatal error, exiting
Apr 17 16:18:36 pfSense ppp[57660]: [wan] IFACE: Close event
Apr 17 16:18:36 pfSense ppp[57660]: [wan] IPCP: Close event
Apr 17 16:18:36 pfSense ppp[57660]: [wan] IPV6CP: Close event
Apr 17 16:18:36 pfSense ppp[57660]: [wan] Bundle: Shutdown
Apr 17 16:18:36 pfSense ppp[57660]: [wan_link0] Link: Shutdown
Apr 17 16:18:36 pfSense ppp[57660]: process 57660 terminated
What is the LCP authorizing with here if there is no SIM? and how is it successful?
With a known-working SIM inserted and router rebooted, exactly the same up until:
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPCP: SendConfigReq #2
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPADDR 0.0.0.0
Apr 17 16:43:24 pfSense ppp[86491]: [wan] PRIDNS 0.0.0.0
Apr 17 16:43:24 pfSense ppp[86491]: [wan] SECDNS 0.0.0.0
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPCP: rec'd Configure Nak #2 (Ack-Sent)
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPADDR 10.88.80.91
Apr 17 16:43:24 pfSense ppp[86491]: [wan] 10.88.80.91 is OK
Apr 17 16:43:24 pfSense ppp[86491]: [wan] PRIDNS 66.28.0.61
Apr 17 16:43:24 pfSense ppp[86491]: [wan] SECDNS 209.244.0.3
...
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPCP: state change Ack-Sent --> Opened
Apr 17 16:43:24 pfSense ppp[86491]: [wan] IPCP: LayerUp
Apr 17 16:43:24 pfSense ppp[86491]: [wan] 10.88.80.91 -> 10.64.64.0
Apr 17 16:43:25 pfSense ppp[86491]: [wan] IFACE: Up event
Apr 17 16:43:25 pfSense ppp[86491]: [wan] IFACE: Rename interface ng0 to ppp0
Apr 17 16:43:25 pfSense ppp[86491]: [wan] IFACE: Add description "WAN"
Aha! we finally have an IP address 👌
And WAN interface now shows as up. 😄
I think connecting the correct pigtails gave enough signal strength to finally work.
Only problem now is the IP is private and NAT'd by the provider, so will have to request a public!
Thanks for your help guys.