No and no. When you "block" your CID (ie; LASS code *67), it's blocked at switching equipment level. The switching equipment recieves this kind of information, but the person on the other end does not. Spoofing caller ID with voIP? Perhaps a few voIP service providers allow that or have bad enough security for that to be possible, but generally that isn't true.
Yes, CID is generally blocked at the terminating switch...BUT the terminating switch doesn't need to pay attention to the presentation bits in the SS7 Initial Address Message (google these terms for more info) IMU. Thus a terminating switch can pass on CID even though *67 (or, as it's also known: Calling Line Identification Restriction) is activated. This isn't usually the case with your average run-of-the-mill switches in your local COs (unless you're ubscribed to CLIRO service. CLIRO = Calling Line Identification Restriction Override) but this scenario (the scenario of the terminating switch ignoring the CPN presentation bits) can and does happen with some cellular service providers and to incoming VoIP gateways. A perfect example of a cellular provider's switches ignoring CPN presentation bits is the old Omnipoint voicemail. If somebody called you with their caller id blocked and they were transferred to your voicemail (cause you didn't pick up or whatever) the voicemail still captured the Caller ID even though the caller id was blocked.
Now with VoIP the terminating "switches" are atually servers hooked up to PRI lines. So it's up to wichever company that's maintaining these gateways to decide whether their equipment will honor or disregard the presentaton bits. Certain VoIP voicemail companies, like K7, ignore presentation bits and capture the CID even if the calling party requested its blockage.
Also, spoofing caller id with VoIP is relatively easy and common. Most providers let you choose your own phone number upon joining. Providers who support the IAX protocol also can give you the ability to change your Caller ID on the fly. Uhm, that's it, I guess.
