To access my voicemail, I have to dial 123.
On the Librem 5, this works if I dial it manually, but if I store it in a contact and dial it from the contact, the phone instead dials +44123, which is incorrect and, more to the point, doesn’t work.
123 is not a valid national or international number. It is a short number that’s only defined within the context of my particular operator’s network, and should never be dialled with any international prefix. It’s kind of like an internal line on a PBX that can be called from inside the system, but not from outside of it.
(Speaking of which: another use-case that would be broken by automatically adding a country code would be if you use a SIM that connects your phone to something other than the PSTN. For example, the Andrews & Arnold SIP2SIM service, which turns a mobile phone into a SIP extension on an arbitrary phone system, with the ability to dial internal-only phone numbers.)
Each time I find a bug with this phone, it turns out someone is already trying to fix it, and this one is no exception. It seems that part of the problem has been the use of the tel: URI scheme to interface between the Contacts application and the Calls application, which does not define a standard way to handle this.