I would like to spam trap calls from telemarketers, etc. I can actually\ndo this in many cases because a lot of telemarketers use easily\nidentifiable numbers. However they do also sometimes withhold their\nnumbers. I cannot routinely block withheld numbers as I also receive a\nlarge number of calls from genuine uk businesses who very unhelpfully\nalso choose to withhold caller id.\n\nI recently read that when a caller withholds caller id this does not in\nitself prevent id information being sent, it just sets a flag saying the\nentity providing the DID (Direct Inward Dialing) service should strip\nthe information before sending it on to the customer receiving the call.\n\nIt also appears that some DID providers for SIP lines do not do this.\nI'm with Sipgate which does appear to strip the information. Does anyone\nknow of alternative DID providers who do not strip the information.