The same endpoints cover one campaign:
campaigns[] on
List phone numbers says
which campaign a number is on,
Search phone numbers and
Buy phone number take an
optional campaignId so a bought number lands on the campaign in one step
(without one it waits in the pool, billed from purchase), and
Assign phone number puts a
pool number, including one you own in Twilio, on a campaign.
Scopes: phone_numbers:read, phone_numbers:write, phone_numbers:release.
See Authentication.