# *21# on iPhone: Resume Call Forwarding URL: https://byshahid.com/blog/resume-call-forwarding-star-21-iphone/ App: Secret Codes: IMEI & Carrier (https://apps.apple.com/us/app/secret-codes-imei-carrier/id6807154322) Author: Muhammad Shahid Updated: 2026-11-04 > *21#: Re-enable forwarding using the number already stored. Turns unconditional forwarding back on using whichever destination number is still registered with the network. If no number is stored the network replies with an error — register one with **21*number# first. - **Code:** *21# - **What it does:** Re-enable forwarding using the number already stored. - **Published for:** AT&T and T-Mobile - **Type:** GSM networks Re-enable forwarding using the number already stored. This page explains what `*21#` does, how to use it on an iPhone and which carriers it applies to. I build **Secret Codes: IMEI & Carrier**, a free iPhone app with 317 checked codes and guides, including this one. If you would rather tap than memorise, [get Secret Codes on the App Store](https://apps.apple.com/us/app/secret-codes-imei-carrier/id6807154322). ## What does *21# do? Turns unconditional forwarding back on using whichever destination number is still registered with the network. If no number is stored the network replies with an error — register one with [**21*number#](/blog/turn-on-call-forwarding-star-star-21-star-number-iphone/) first. ## How do I use *21#? - Open the Phone app and tap Keypad. - Type *21# exactly as written. - Press the green Call button and wait for the result. ## Which carriers does this apply to? | Published for | AT&T and T-Mobile | | Type | GSM networks | | Good to know | GSM networks only. Requires a previously registered forwarding number. | _Screenshot: The Secret Codes detail screen shows the steps, the carriers and an Open in Phone button._ ## Related call forwarding codes - [#21#: Pause Call Forwarding](/blog/pause-call-forwarding-hash-21-iphone/) - [*#61#: Check No-Answer Forwarding](/blog/check-no-answer-forwarding-star-hash-61-iphone/) - [##21#: Turn Off Call Forwarding](/blog/turn-off-call-forwarding-hash-hash-21-iphone/) - [**61*[number]#: Forward When You Don't Answer](/blog/forward-when-you-dont-answer-star-star-61-star-number-iphone/) - [**21*[number]#: Turn On Call Forwarding](/blog/turn-on-call-forwarding-star-star-21-star-number-iphone/) - [**61*[number]**30#: Set Ring Time Before Forwarding](/blog/set-ring-time-before-forwarding-star-star-61-star-number-iphone/) See all [call forwarding codes](/blog/iphone-codes/call-forwarding/) or [every category of iPhone codes](/blog/iphone-codes/). ## How Secret Codes helps Secret Codes keeps this and every other entry a search away. Pick your carrier once and each entry says whether it is published for your line. You can save favourites, add a private note, and record whether a code worked on your line. This entry is part of Secret Codes Pro. **Secret Codes: IMEI & Carrier** is free on the App Store: https://apps.apple.com/us/app/secret-codes-imei-carrier/id6807154322 ## FAQ ### What does *21# do on iPhone? Re-enable forwarding using the number already stored. Turns unconditional forwarding back on using whichever destination number is still registered with the network. If no number is stored the network replies with an error — register one with **21*number# first. ### What are the steps for *21#? 1. Open the Phone app and tap Keypad. 2. Type *21# exactly as written. 3. Press the green Call button and wait for the result. ### Where do I use *21#? On the keypad of the Phone app. ### Do I need to press Call after typing *21#? Yes. Type it on the Phone keypad, then press the green Call button. ### Is *21# a hidden or secret code? No. It is a standard GSM code, handled by the network rather than by a hidden menu on the iPhone. ### Which carriers does *21# work on? It is published for AT&T and T-Mobile. GSM networks only. Requires a previously registered forwarding number. ### Does *21# work on Android phones too? GSM codes are a network standard, so they generally behave the same on any phone on a network that supports them. ### Will *21# work outside the US? It depends on the network you are on. GSM codes are a standard, but each network decides which it supports. ### What if *21# does not work on my iPhone? Check that it applies to your carrier first, because carriers decide which services they offer and can change them. If it should apply to your line, contact your carrier. ### What is related to *21#? #21#: Pause Call Forwarding. Switch forwarding off but keep the number saved. ### What else is in this category? *#61#: Check No-Answer Forwarding. See where calls go when you do not pick up. ### Can I find *21# in an app? Yes. Secret Codes, a free iPhone app, includes it with its steps and carrier details, as part of Secret Codes Pro. ## Sources - [3GPP TS 22.030: Man-Machine Interface of the phone](https://www.3gpp.org/dynareport/22030.htm) - [Verizon Support](https://www.verizon.com/support/)