I am in the USA and these are USA numbers. The one above is to ionos.com customer support. Another number that doesn’t work is someone I know. I can put the sim card into another phone and that phone will dial those numbers. Other phone numbers work fine on this module,
VOLTE is enabled and works fine on this module for most numbers. One thing that might be a clue. When I move the SIM card into another phone, the other phone also cannot dial that number the first time, but then it works when I retry it. Putting the SIM back in this HL7648 module, the old problem is back. This problem might be a configuration issue between the module and the SIM.
My problem is occurring with SIM is for an MVNO using AT&T network. I went to an AT&T brick-and-mortar store and borrowed an AT&T SIM. It worked fine to call the above problem number. There is some problem regarding the MVNO SIM I am using with this modem module, and it doesn’t happen if I use the AT&T SIM. I have contacted the MVNO regarding this.