Regarding unidentified calls on your caller id (and I'm quoting a telephone employee here):

"The auto-dialer has nothing to do with it. The reason that your outgoing solicitation calls are displayed as "Unavailable" or "Out Of Area" is due to their intentional use of the outdated "MF-trunking" (multi-frequency or "in-band signalling") technology, which is NOT compatible with the current telecom industry standard, Signalling System 7 (SS7). SS7 is what allows the "CLASS" features (Caller*ID,Repeat Call, Return Call, Call Block, etc.) to work. Even though SS7 was introduced in the late 1980's and is fairly ubiquitous by now, the telemarketing industry purposely sends all their calls (local & LD) over these antiquated toll circuits to avoid detection/blocking by customers with Caller*ID or related blocking technologies. The bill in Congress attempts to outlaw this sorry practice. The ONLY legimate use of remaining MF-trunking in this day and age is at the thousands of smaller CO's in rural areas served by independent telcos who haven't done network or switch upgrades yet. Even the wireless companies have had modern SS7 networks for a few years!"

However, Call Blocking and Anonymous Call Rejection may help. Call your local businss office to find out what is available in your state.