There's always been a problem on Orange (UK) that when you receive a voicemail notification (which on any other phone would turn on the spool icon), you see nothing on the 3650 screen (and hence have no knowledge of the waiting voicemail).
Well, this is now fixed by Nokia 😃
The new v4.13 firmware which was released last week includes the following line:
* Class 0 SMS with voicemail waiting indication flag handled correctly
This results in the alerts working correctly.
I can personally confirm that this version should be available to all NSCs (Nokia Service Centres) and as long as you can persuade them to actually perform the work (always a challenge in my opinion) this will fix the problem (at least it did for me). You obviously might need a receipt to prove the phone is in warranty (although all 3650s should be, as it's not been available for over 12 months in the UK yet)
Hope this helps someone, it's made the 3650 a phone I can consider keeping long term now.
Strangely, a lot of Line 2 (ALS) functions are available in the phone (including indicating which line has voicemail) although the phone part is not aware of Line 2, and hence I can't make calls on it - I'm considering sending the phone off to Nokia to enable Line 2, or removing it and spending the money elsewhere.
Steve