Masked Calling

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Masked calling is a technique used in ecommerce to protect buyers' and sellers' personal phone numbers private. It uses a short-lived phone number for each party, allowing them to communicate seamlessly during a specified time period. After the time period has expired, the numbers are recycled and reassigned to other parties on the platform, which helps keep transactions from happening outside the platform. 

Masked calling refers to the technique made possible by Voice APIs like Twilio where a developer can set up phone number proxies to keep parties from knowing each other's phone numbers during a call. The same technique can also allow the parties to send SMS to each other without revealing their personal phone numbers.

The basic technique involves using an intermediate number assigned using Twilio to forward the call to the user's real number. So the customer may see number AAA-AAAA, but behind the scenes, AAA-AAAA is being forwarded to the seller's true number, BBB-BBBB. When the seller's phone rings, she also sees the caller ID as AAA-AAAA when the buyer's true number is CCC-CCCC. Applications using masked calling techniques usually leave the numbers assigned for a period of time (say, the length of the taxi ride plus a couple hours in case the rider left her backpack in the car), after which the numbers are recycled and reassigned.

Assembling a pool of numbers with Twilio is simple and straghtforward, as is the number assignment and call forwarding.

More resources:

- Read how Uber uses Twilio for masked calling

- Learn why you might want to use masked calling

- See the basic steps to build masked calling

- Sign up for Twilio and explore this code tutorial on masked calling with C#

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