I believe MGuzzy is right. There's no way to get it back. As a workaround, you can open the Messages application and set your voice mail number in it's Voice Mail options. That will have the affect of programming the number into the "1" key on the keypad. Simply hold down that key for 2-3 seconds, and the 7135 will automatically dial the number that you programmed in the Messages application. That's the way I check mine.

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Michael