I gather the voicemail callback number is stored on the SIM card. Any android SIM card manager app tells me the Vertical service code on the SIM card for voicemail is *68, which seems to be "Activate call forwarding on busy" according to a google search. *98 is apparently the right one since I can change it to that in my dialer and long pressing 1 calls voicemail properly. However, when I reboot my phone, the number goes back to *68. My change isn't preserved across boots.
Is the voicemail number really stored on the SIM card, or somewhere else? How can I make it stick across reboots of my android phone?
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I can change the voicemail callback number to +14168216549 or *98 using those instructions and both work for long press 1 to access voicemail. No problem there. The problem is, when my phone is restarted it goes back to *68 and I have to change the voicemail number all over again. I was kind of hoping there would be a method to make the change permanent across reboots. My phone is rooted because it was the only way to change the incorrect APN settings. That entailed editing an apns-conf.xml file. Is the voicemail callback number also stored in a database or file I can edit?
@cbsewell set back the VM number then go to call forwarding and change "When unanswered" and "When unreachable" phone numbers to your voicemail number and see if it sticks this time.