The answer to all of the above is "Yes, but..."
The general rule is that any telecommunications carrier must port its customer's number to another telecommunications carrier that has a presence (i.e., has telephone numbers) in the same rate center.
Now for the "buts": Telecommunications carriers include cellular/PCS operators, ILECs, and CLECs. Some VoIP service is offered by telecommunications carriers, and the number portability requirements would apply to their service.
Some VoIP service is offered by companies that are information service providers, not telecommunications carriers, such as Vonage. Since they aren't telecom carriers, they generally don't interconnect directly with the PSTN and don't get numbers directly from the numbering administrator (or the pooling administrator). So Vonage et al. don't have numbers of their own in any rate centers. Instead, Vonage et al. buy numbers from telecom carriers, presumably CLECs, who obtain numbers from the numbering adminstrator (or the pooling administrator) in various rate centers. If Vonage has a deal with a CLEC such as Covad (just using Covad as an illustration; I don't know whether they have such a deal) to get numbers in a particular rate center, then numbers in that rate center would be portable to and from Vonage via Covad; this should be true of wireline and wireless numbers in that rate center.
Non-wireline carriers, including wireless (cellular/PCS) and VoIP providers, don't need to have numbers in every rate center where they have customers, unlike wireline carriers, because they don't need to have wires going from a switch in the rate center to the customer. Wireless carriers typically select a subset of rate centers that is big enough to avoid toll charges from most "local" calls to their customers. For a simplified example, if rate centers A, B, C, and D all have wireline calls amongst them rated as "local", a wireless carrier only needs numbers from one of them.
What this means is that if the wireless carrier gets numbers from rate center A, wireline customers in rate center A will be able to port to wireless and vice versa. Wireline customers in rate centers B, C, and D will not be able to port to or from wireless because the wireless carrier isn't present in their rate center.
I assume that the same is true to some extent of VoIP providers, but given their strategy of seeking ports of wireline phone numbers, they have good reason to get numbers (via a CLEC) in each rate center in densely populated areas, while wireless carriers don't have a compelling reason to do so at this stage, since they aren't actively promoting ports of wireline phones.
There are exceptions to all rules. Where the FCC is concerned, there are rural exceptions to all rules, since rural telcos are never held to the same standards as others. If you live in a rural area, don't hold your breath waiting to port your number from or to a wireline phone.
Regarding wireless number portability:
Michael D. Sullivan Bethesda, MD (USA) (Replace "example.invalid" with "com" in my address.)[TELECOM Digest Editor's Note: Mr. Sullivan, am I correct in saying another reason for denying portability of a number is because a customer has a delinquent bill with the carrier he is attempting to port _from_ or out of? I think I saw somewhere that carriers have that protection or recourse available to them, i.e. if you don't pay your bill, you cannot have the number. True or false? PAT]