Wouldn't that depend on the type of phone you have and the version of the OS, if you want to do it on the phone? Since you post on the LG forum it seems that's what you want. Can you tell that?
And wouldn't it depend on the cell phone provider how to do it on their network? Then you ask their customer service.
Kees
On my mobile plan, Capt. Telstra charges more than a dollar for me to access my voice mail. No, sez I, I'll leave a message telling the caller I won't be accessing voice mail and why. How do I do this - I can't find how to in the manual?

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