The difficulties won't "derail" VOIP. The VOIPS will have to spend some money maintaining the appropriate customer databases and then develop a protocol to transmit that information 911 centers. That requires some cost and effort, but it is not impossible as long as the VOIP owners understand and accept their responsibility and liability in this matter.
I suspect it will increase the cost of providing VOIP service and raise fees a bit, but since the protocols and databases should be standardized, the computer costs could be spread out among many VOIP customers, so it won't be a big deal.
What I think a concern should be is service reliability. On the next virus/worm attack when the Internet is flooded with messages and intermediate switching/relay points can't keep up, it's possible VOIP telephone service won't be available or be difficult to use. I don't know how VOIP handles "traffic jams" where packets are delayed en route. Also, if some business which is dependent on VOIP for its voice has major server problems will voice traffic be disrupted?
[TELECOM Digest Editor's Note: Well Lisa, since we are chatting about 'service reliability' and how important it is, what about when a place like California has an earthquake now and then, or now and then in New York City when an airplane crashes into a tall building and all the people get excited and stirred up and all everyone jumps on the phone at one time bringing the phone system to a screaming halt with all the dialtone missing and the switching capacity totally used up? Or, about every 14-15 years on average when a telco central office burns down, and there is no phone service at all for a few weeks or months, i.e. New York City, middle 1970's; Hinsdale (Chicago), Illinois in 1988. Telco has been known to have its share of 'traffic jams' also, so my question is, considering how many business places are dependent on telco, how do they manage to get by when telco has an incident like that? You know, I guess, that the events in NYC on 9-11-01 damn near wrecked the central office serving lower Manhattan from the size and fury of the 'traffic jam' as people found out what was happening. Do we dare trust something like telco when reliability is important? PAT]