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Open the SMS message the contact sent to you, scroll up and highlight the phone number, press the menu key and select Copy.
Open your Address Book on the device, highlight the contact that the number is associated with, press the menu key and select Edit. Scroll down to Mobile Number and delete what you have in there, then press the menu key and select Paste.
See if that clears your issue up.
The difference between stupidity and genius is that genius has its limits.
When you take things for granted, the things you are granted, get taken.
Even a mosquito doesn't get a pat on the back until it starts to work.
Too many people miss the silver lining because they're expecting gold.
[BES 5.0.3 / GroupWise 2012 HP2]