Does Steam accept a VoIP number for Steam Guard and account recovery?

What Steam says

• Steam Support

  “We are unable to accept new VoIP phone numbers on Steam due to them not meeting our security requirements. If your phone number is blocked because it's considered VoIP you will need to find a mobile or prepaid phone number to use on Steam.”

  https://help.steampowered.com/en/faqs/view/7EFD-3CAE-64D3-1C31

• Steam Support

  “Select carriers use VoIP technology in their cellular plans and we are unable to support these.”

  https://help.steampowered.com/en/faqs/view/7EFD-3CAE-64D3-1C31

Three details in there are worth reading twice.

• Prepaid is fine. Steam names “a mobile or prepaid phone number” as the fix. You don't need a contract.
• Some real carriers fail. Steam says its check rejects carriers that run their cellular plans over VoIP. A phone from a carrier store isn't automatically safe.
• The rule is about new numbers. Steam doesn't say what happens to a VoIP number that's already on an account. We wouldn't count on one for recovery.

Steam tells you up front: “Our system will notify you when you enter your phone number if we consider it to be a VoIP number.” If you think it got your number wrong, the FAQ says to contact Support with the “Help me with my issue” button.

Why the number matters on Steam

Steam is clear about what the phone number is for: “You can use SMS messaging to reset your password, or transfer your Steam Guard Mobile Authenticator from one phone to another.” And there's one slot: “only one phone number can be associated with a Steam account at a time.” (Steam)

Backup codes need it too. To get them, you “have to enter the SMS code that is sent to your phone number.” A number that can't receive Steam's texts quietly closes every recovery path Steam offers.

The situations people actually hit

New or wiped phone, same number

The easy one. Steam's advice: “If possible, you should contact your wireless service provider and get a replacement phone with the same phone number.” Then move the authenticator using a text code. Expect “a 2-day trade and market restriction” afterwards.

You're about to lose the number

If the old number is going away, Steam says to remove the authenticator before it does. That locks trading and the Community Market for 15 days, and Steam recommends transferring the authenticator instead when you can. Either way, change the number on the account while the old one still gets texts, not after.

The texts just don't come

Two causes from Steam's own list catch people: “Our text messages can come from a 6 digit phone number, please ensure that your provider supports this.” And: “Steam will also stop sending SMS messages if too many have been sent to you, so waiting a few minutes to an hour may allow messages to come through again.” Pressing resend ten times makes it worse.

No phone and no recovery code

Then it's a support ticket: “If you no longer have access to your phone and don't have your recovery code, you'll need the assistance of Steam Support.” Write your recovery code down today. It's in the app, on the Steam Guard page, under the gear icon.

Steam's own alternatives, and their limits

The mobile authenticator is the strong option, and it works offline: “Your phone does not need to be connected to the Internet for the authenticator to generate a code”. But it needs a phone. Asked whether you can use it without one, Steam says: “Not at this time. A supported phone is required.” Steam Guard can also send codes by email instead (Steam), and backup codes are the emergency fallback. Steam says to print those: “Don't take a screen shot of them.”

Why a number only you use matters here

Steam treats the phone number as part of your identity: “Accounts with the same phone number may be treated as the same identity with respect to the Steam Subscriber Agreement, policies, or restrictions.” Its FAQ adds that a VAC or game ban on an account can extend to other accounts on the same number. A number that someone else has used on Steam can bring their history with it. A number that's only ever been yours can't.

When a real mobile line is the answer

When Steam rejects your number as VoIP and you don't have a mobile number you'll keep for years: you moved country, your old carrier number is gone, or you're tired of the recovery number being whatever SIM is in your phone this year. A Cleat line is a real US mobile number that receives texts, held by one identity-verified owner, for $24.99 a month. It's receive-only. Steam's check also rejects some carriers' mobile plans, so no provider can honestly promise Steam accepts a given number, us included. Why line type decides this.

If you're abroad

Enter the number “in international format (with '+' and your country code first)”, and check the country Steam guessed. Steam also says “Telegram is sometimes used as an alternate delivery mechanism” in countries where Telegram is common, if the number has an active Telegram account, so look there if a code seems to be missing. Living outside the US long-term? Cleat for expats.