This problem (and telemarketing in general) is incredibly easy to solve, especially if you are Google or Apple. In fact it's almost a disgrace that they don't.

This problem (and telemarketing in general) is incredibly easy to solve, especially if you are Google or Apple. In fact it's almost a disgrace that they don't. Back in the day, did this with the apps for local.ch in Switzerland ( some fluffy details here: https://tel.local.ch/en/advertising-calls https://tel.local.ch/en/advertising-calls ) which something like 40-50% of the Swiss population have installed on their phones. As a Yellow pages phonebook app we provided an "Incoming Call" lookup service against our search engine of Swiss business phone numbers, so we could see who you received calls from (data which we treated as strictly private). These types of robocallers (and telemarketers in general) were really easy to spot in logs - you see a number that's been calling many different people but _wasn't_ in our official database of businesses (we had good coverage of all businesses in Switzerland), we'd flag it our users with "We don't know this number but we suspect telemarketing" leaving the user to decide whether they wanted to call back or not. The Google Places API or the Yelp API ( https://www.yelp.com/developers/documentation/v3/business_search_phone https://www.yelp.com/developers/documentation/v3/business_se... ) would probably suffice for the same purpose. The only way to get round this is for robocallers to rotate the numbers they're using with a very high frequency so they don't "peak" in the logs but that can get expensive for them. What's nice is this approach is also dynamic - you don't need an official database of blacklisted numbers. You just need a big enough sample of users with your app installed and you'll catch Robocallers as soon as they start peaking in any logs. Apple and Google have way more insights into who's calling who than this (e.g. number of rings, email signatures, the users address books, which numbers have been blocked and a ton of analytics) which could be used to kill telemarketing for good. Given the solution is so simple, it really surprises me they don't.