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?