I know this thread is a few weeks old but answers should still help.

3.0 does not have dns programming. It does have default gateway address or "router" address as it is called.
You should be able to get the admin program from the ftp site.
3.5 firmware had a bunch of bugs, depending on the revision. I took all my 3.5s to 4.0 if the cpu card was new enough.

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"Old phone guys never die, they just get locked in some closet with an old phone system and forgotten about"

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