email, at least, you can fully implement your own antispam solution in whatever way you want at one extreme, you can just point the mx records for your domain

email, at least, you can fully implement your own antispam solution in whatever way you want at one extreme, you can just point the mx records for your domain at office365 or gsuite or similar and let them handle it at the other extreme, you can point the mx records at your own mailserver you admin yourself and do absolutely anything you want with the incoming smtp mail flow for antispam measures, sorting, filtering, categorization, risk analysis. the ordinary person even if they work for a telecom cannot implement their own phone number at one of the most fundamental levels of the pstn, because they don't run their own ss7 switch. if you control your own DID and interface with it from a sip trunk to a trusted provider, running your own voip system, you can do a lot with custom routing/antispam measures on incoming call flow, but nowhere near to the extent that you can with email.