When adding new inbound phone numbers in Fastcall, the phone numbers must be provisioned by Fastcall. If you have existing numbers in Twilio you will need to email Twilio support to ask to have the numbers moved to the Fastcall subaccount. Once added to the Fastcall subaccount, you will not be able to control these in Twilio (not that you would want to.) You will see a Fastcall logo next to the number to show that the number is now controlled by Fastcall. Good.
NOTE: Your Twilio parent account SID and connected account SID are listed under the Twilio section of Fastcall. You should give both these accounts SIDs to Twilio when discussing your Twilio account.
When transferring numbers to Twilio – or moving numbers from a Twilio parent account to the connected account used by Fastcall – keep in mind that these are really two different accounts. Fastcall created a connected account used for billing purposes only. Phone numbers cannot exist in both accounts and can only be transferred internally by Twilio. For security purposes, Fastcall does not have API access to your parent Twilio account. You have only granted billing rights.
In the Fastcall app under advanced settings, there is an option to sync Fastcall with Twilio (resync actually). Hit this, and the transferred numbers will now appear in the Fastcall phone tab ready to be assigned. The phones will be moved by Twilio from the parent account to the connected subaccount. And once in the connected subaccount, the phones can be managed by Fastcall. Make sense?
In our post on Inbound Call Routing we discuss this process and give a tip on porting numbers to Twilio. If you plan to port a number from another carrier to Twilio you may want to verify that your current carrier will release the number. Once confirmed, another good idea to provision a test number first in Fastcall. Better to test with a throwaway number, then go through the transfer process only to find an issue that could have been discovered via a quick test.
OK, that said, use this form on Twilio to begin the transfer process.
You should also review this Twilio FAQ on number porting.