You can activate Allo on your normal number and still use a local SIM for data.
In addition to being linked to your Google account, Allo is tied to your main phone number. That makes things tricky if you use multiple devices — unlike Hangouts, there's no easy way to use it on multiple phones at the same time right now. And the phone number tie-in might seem to make things difficult for travelers too — specifically being stuck on one phone number with the associated roaming costs when traveling abroad.
Fortunately, there's a simple workaround.
Allo is heavily inspired by WhatsApp, and the way it handles SIM swaps is basically borrowed from the rival service. Activating Allo on a new device is what ends your previous session, not changing the SIM in your phone. And even if you swap SIMs while you're traveling, Allo will remain activated on your old number — just so long as you don't sign into Allo with that number on a different device.
So if you want to use a local SIM when traveling, simply do the following:
- Activate Allo on your main (home) number using SMS authentication. (Chances are you've already done this.)
- Swap your SIM to a local one when you arrive at your destination.
- Continue using Allo as normal. You'll receive Allo messages sent to your home number while using the local (foreign) network for data, calls and texts.
If you're logged out for whatever reason, you'll be able to log back in by receiving Google's authentication text message to your main phone number. (You don't necessarily need your main SIM in your main phone to do this, just as long as you can receive the SMS.)