I noticed today that the phone automatically add my area code 510 to whatever phone number I dial. Therefore, it becomes 510 plus the first 7 digits I dial.
Jacob was using an example number. https://en.wikipedia.org/wiki/867-5309/Jenny
I've seen some Panasonic cordless phones that automatically will insert an area code into a dialed number. Perhaps your phone is doing the same? Do you have a different phone that's not programmable that you can try?
This is helpful in some areas, like the DC suburbs, where local calls require an area code but are dialed without an initial "1". CA requires a 1 if the call is in a different area code.
Speaking of 510, effective June 22, even if you're calling another number in the 510 area code, you will be required to dial 1 + 510 + 7D. This is because the new 341 overlay code becomes effective in July.