It seems the folks in Baltimore want to tax Vonage.
The same thing happened a few years back in California so I don't see this as a battle that won't stop happening, especially as more and more of city's tax bases erode with new technology.
For example, the tax revenue generated from coin boxes/pay phones is pretty much a goner due to the cell phone market. All cities are trying to do is recover what they are losing by replacing tax that would have been collected on one product/service with what is replacing it.
Again, the DUCK test applies. Unless something is so different, why should the way we treated it's predecessor be handled any other way. That said, IM based phone service that doesn't use the PSTN is not the same in my book and as such needs new and different tax and FCC handling. The tax on the sale of minutes that can terminate to the PSTN is handled by sales tax, and states have a way of dividing that up.
As such, the entire way taxes are handled in the USA may also need major reform as the current in place system doesn't have any way of adapting to a world where technology is moving so fast.