Can someone, preferrably from Comcast, explain why international calls cannot be screened? There seems to be no technical reason why this would be --- since the numbers are, well, just numbers.
I have seen a vague reference to legal issues, but would appreciate a more detailed response.
Seems like an opportunity for a clever person to insert a programmable box between your main phone jack and your phone system. One could screen an unlimited quantity, regardless of origin, or set up a white list.
In the US, they were all mostly installed in the 30s through 80s, and with all of North America on a unified numbering plan, most have been hard-coded to only work with 10 digit numbers (and thus assume all numebrs are "domestic" North America.
Now, newer switches do have the leading "1" in there, but it's still very, very memory intestive in the box, and most of the memory is filled with routing tables to ensure your call gets to where it's going on the hardware phone network. So, usually, features available are dependent on total memory and usage. For example, you can block 25 numbers if you disable anonymous call blocking. You have 2048 bytes to work with, which of the 30-40 phone features you want on your phone need to be managed accordingly.
Add tot he fact that Comcast is VoIP rather than pure Copper networks, it has some fun issues with the implementation of SIP and SS7 interfaces. In short, the incoming number via SIP/VoIP has no guarantee about source Identity, which is why many implementations will just bail and say "unknown caller" or "number unknown" because the translation to-from physical/software environements wil butcher the identity and each passing switch potentially tries to process the data. So, we see things like 0177585222 (presented as a domestic EU number, but this is useless at the country code is unknown), 6242223333 (Philappines, but presented as a US 10-digit, because the INTL flag isn't being parsed), and the APIs and systems all assume 10digits = US (which is false, many fully qualified numbers are only 10-digits, like Belize. the entire country is on 7-digit dialing, plus the 3-digit country calling code....)
In short, the US hardware, and software for the last 50 years has been very skewed towards cheapness, lack of hardware upgrades (due to no regulations forcing companies to meet ever increasing qualities of service.), and the overall lack of people calling US/CAN/Carribbean (and until the mid 90s Mexico was just another Area Codes 905 = Mexico City, 706 = NW Mexico. (tehy since switched to their own phone numbering system outside the common North American Plan, and thus country code +52 was born).
But, without any government mandate forcing all telecom providers to privode minimum classes of service and obligations, like they have in EU, this situation isn't going to be changing anytime soon. There's no incentive for any business to spend all the money required to update 100 years of infrastructure without a business case to justify the capital expenditures for it.