How Google's chat app handles phone numbers, multiple devices and switching phones.

Allo is tied to both your Google account — for intelligent predictions and Google Assistant — and your phone number, for helping friends and other contacts find each other. But the phone number requirement also introduces a few limitations in the way you can use Allo.

Here's a thorough breakdown of how things currently work.

Can I use Allo without a phone number?

No. Allo is tied to your Google account, but it also uses your phone number to discover contacts. You'll need to activate Allo by receiving an authentication code by text message during the setup process. You can, however, use Allo — including the Google Assistant feature — without a Google account. But if you don't link your account, your Assistant interactions won't be saved when you switch phones.

Can I use Allo on more than one phone at once?

No. Right now signing into Allo on a second phone signs you out on the first. You'll see a message like this:

Allo second device message

You'll also need to re-authenticate via SMS on each new phone you activate. (Just like WhatsApp.)

What happens to my chat history and group chat memberships when I switch phones?

When you sign into Allo on a new phone, your group chat memberships — but not your chat history — will go with you. Allo chats live on your device, not in Google's cloud, and there's currently no way to back up chat history, like there is with WhatsApp. (Any undelivered messages will appear on your new device, however.)

It's a pretty major oversight, and a feature we'd expect to be added to Allo before long.

Can I use Allo on tablets?

Android tablets appear to be unsupported through the Google Play Store at present. Google lists iPad support on its official site, so it's likely Android tablets will be coming soon to the platform. However, if and when this happens, the same phone number restrictions are likely to apply.

Can I use Allo on desktop, Chromebooks or the web?

There's no desktop app or web interface for Allo yet. In theory you could use Chrome OS's Android app support, when it launches, to use the app on your Chromebook, but even then you'd have the same phone number restricitons. (Logging in on your Chromebook would sign you out on your phone.)

Do I have to use Allo with the phone number of the SIM in my phone?

Not necessarily. As we discuss in greater detail in this article, you can activate Allo on one phone number, then switch SIMs and continue using the first number for Allo messages.

What if my phone number changes?

Unregister message

You can unregister your phone number through the Settings menu. Unregistering your phone number will remove you from any groups, and permanently delete your chats. Your Google Assistant interactions won't be deleted, so long as you've also added a Google account.

If you're changing phone numbers permanently — for example changing carriers — you'll want to make sure you unregister your number beforehand. That's because Allo messages are tied to your phone number, and in theory your old number could be allocated to someone else in future.

There's currently no way to port chat history or group chat memberships between numbers, as there is for WhatsApp. (Because right now there's no way to transfer or back up chat history at all.)