Keeping control of client phone numbers on Synthflow, and when you move.
MigrateBy CenterfyUpdated
The short answer
Control of a phone number sits with whoever holds the account it lives in. Synthflow's documentation describes three cases. A number bought inside Synthflow lives in Synthflow and belongs to the workspace that bought it, so a number your agency bought and assigned to a client's subaccount is still your agency's number. A number connected through Twilio stays in the Twilio account it came from. A number on a SIP trunk stays with your carrier. The reselling change did not alter any of this, but it is the first thing to map before you change platforms: Twilio and Telnyx numbers connect directly to Centerfy, while numbers bought inside Synthflow need a conversation with Synthflow about whether they can be moved.
Three places a Synthflow number can live
| How the number got there | Where it lives | Who controls it |
|---|---|---|
| Bought in Synthflow (US, Canadian and Australian numbers) | Synthflow | The workspace that bought it. Synthflow recommends purchased numbers for testing and simple setups. |
| A Twilio account connected to Synthflow | Your Twilio account | Whoever holds the Twilio login. Synthflow routes the calls; the number stays in Twilio. |
| A SIP trunk or PBX, which Synthflow lists as an Enterprise feature | Your carrier or PBX | Whoever holds the carrier account. |
Synthflow's own advice is to validate call flows on a purchased number and, for production, to move to Twilio or SIP “so you keep control of your numbers, regional rules, and configuration”.
Agency or client: who owns a number in a subaccount
This is the part that matters for resellers. Synthflow's documentation is explicit:
- A number your agency bought or imported and then transferred to a client's subaccount is still your agency's number. The client can use it but cannot delete it.
- Purchased numbers stay on the parent account's monthly subscription while the subaccount uses them.
- A number the subaccount buys itself belongs to the subaccount, which can delete it or cancel its subscription.
- Deleting a subaccount returns transferred numbers to the parent account.
- If your agency workspace uses its own Twilio integration, importing numbers into subaccounts is not supported. Each subaccount's Twilio credentials are managed from its settings instead.
So if your agency supplied the numbers, your agency controls them. That is convenient until a client leaves and asks for their number, or until you want to change platforms. Decide now, client by client, whose account each number should be in.
How to check each client's numbers
| Check | How | What it tells you |
|---|---|---|
| Which numbers each client uses | The Phone Numbers tab in each Synthflow subaccount. | The full list of numbers in use, client by client. |
| Purchased or connected | Your Synthflow billing portal lists subscriptions for purchased numbers. Your Twilio console lists Twilio numbers. | Where each number lives. |
| Who holds the carrier login | Log in to the Twilio or carrier account yourself. | Whether the agency or the client controls the number. A number in an account you cannot log in to is one you do not control. |
Moving numbers to Centerfy
Numbers in a Twilio account
This is the simple case. In the client's Centerfy sub-account, open Settings, then Integrations, choose Twilio under Phone Integration and enter the Account SID and Auth Token. Then open Phone Numbers, click Import Number and enter the number. One imported Twilio number handles both AI calls and SMS, and any A2P 10DLC registration stays with the Twilio account. Do the import when you are ready to switch that client, and place a test call straight away.
Numbers in Telnyx
The same steps with Telnyx selected as the provider, using your Telnyx API key and secret. Imported Telnyx numbers work for voice and SMS.
Numbers bought inside Synthflow
Synthflow's documentation explains how to buy, assign and delete purchased numbers. It does not describe porting one out to another carrier, and we will not claim that it can or cannot be done. Ask Synthflow support in writing whether a specific number can be ported and what they need from you. Until you have an answer, do not delete the number: Synthflow says deleting a purchased number also cancels its subscription. If a number cannot be moved, buy a replacement in Centerfy, where you choose the area code and check the number's spam reputation before purchase, and update the client's website, Google Business Profile and ads.
Numbers on a SIP trunk or another carrier
Centerfy connects to Twilio and Telnyx. A number with another carrier is ported to one of those first, and stays with its current carrier until the port completes.
Centerfy AI numbers and SMS
Numbers bought inside Centerfy are dedicated to AI agent calls. For business texting and manual calling, Centerfy's help centre says to connect your own Twilio or Telnyx number, which carrier registration rules require. An imported Twilio number covers both AI calls and SMS.
Frequently asked questions
Who owns a phone number in a Synthflow subaccount?
Did the reselling removal affect phone numbers?
Can I port a number I bought in Synthflow to another provider?
Can I use the same Twilio number on Centerfy?
What happens to a client's number if I delete their Synthflow subaccount?
Does Centerfy work with carriers other than Twilio and Telnyx?
Should the agency or the client own the number?
Will callers notice a move?
Sources
- 1.Synthflow documentation: Phone Numbers Buying numbers, importing custom numbers over SIP, bringing Twilio numbers, number ownership and deleting a purchased number. It does not describe porting a purchased number out. Read on November 5, 2026.
- 2.Synthflow documentation: Telephony The table of where numbers live for each setup, and the advice to move to Twilio or SIP for production. Read on November 5, 2026.
- 3.Synthflow documentation: Products Importing agents, workflows, phone numbers and actions into subaccounts, and who owns a number that has been transferred to a subaccount. Read on November 5, 2026.
- 4.Synthflow documentation: Subaccounts What a subaccount is, that minutes come from the agency pool, that a subaccount cannot be moved between agencies, and what happens on deletion. Read on November 5, 2026.
- 5.Synthflow documentation: Twilio Numbers stay in Twilio while Synthflow routes the calls; Twilio subaccounts for delegating a number. Read on November 5, 2026.
- 6.Synthflow documentation: Reselling Synthflow's own account of the removal: what stopped on September 15, 2026, who is affected, what stays the same, and how to track and bill subaccounts now. Read on November 5, 2026.
- 7.Centerfy help centre: import your Twilio numbers The steps to connect a Twilio account and import numbers into a Centerfy sub-account.
- 8.Centerfy help centre: import your Telnyx numbers The steps to connect a Telnyx account and import numbers.
- 9.Centerfy help centre: buy and assign AI phone numbers Buying AI numbers by area code, reputation checks, and Twilio or Telnyx for platform SMS.
Centerfy publishes this guide and offers an alternative to Synthflow. Synthflow is an operating company; statements about it are limited to the sources above, read on the dates given, and its product may have changed since. Descriptions of other vendors summarise their public documentation. Source: https://centerfy.ai/resources/synthflow/phone-numbers