The KX-T7030 as well as the KX-T7730 will work with your KX-T30810 system. You will need one at extension 10 to program your system. (Download the manual) Then you can program it so that your single line phones directly pick up a CO line or dial tone. (That dial tone you hear now is intercom dial tone.) If the 7030 doesn't work, well, it's defective. Deal with it as you may but I would want it replaced or my money back. I would send that KSU back too if you have problems with it starting. None of this is worth fixing, you'll never find service information and it's cheap enough to just throw away.

-Hal

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