Yes. The data SIM can do anything other than "regular" calls and SMS. Messaging apps all use data to do their thing, so they'll work fine. That said, if your messaging app requires SMS verification (e.g. Whatsapp or Signal), you'll have to have the initial verification SMS sent elsewhere since the data SIM doesn't have a phone number.

Can you explain further how to get the data SIM to work with WhatsApp or Signal then? I would be interested in using the data sim with an iPad.

What problem are you facing getting WhatsApp to work? Assume this is with a device that WhatsApp works on with another SIM, Fi or otherwise?

WhatsApp and Signal are tied to a phone number and can be installed on exactly one device at a time; installing on a second device will kick the first one off. So if you activate the app on your iPad, it will deactivate on the phone you used to have it on, and re-activating on the phone will kick the iPad off, etc etc.

If you want to use either app on an iPad with a data SIM, you'll still have to have the verification SMS sent to a phone with a 'real' SIM (any carrier) but can then type in the code on the iPad to activate the app.

This is sort of an oddball use case--I'm not sure in what situation it's the best option. Maybe if you've got a phone that's SIM-locked to a carrier other than Fi or T-Mo or doesn't support the LTE bands for where you're going, you could move your WhatsApp or Signal account to the iPad before leaving home. But if your phone can use the data SIM, it's a lot easier just to take out your (non-Fi) carrier SIM and pop in the data SIM. WhatsApp and Signal do not kick you out when you switch SIMs--they'll stay logged in to the account tied to the old SIM.

It's also possible to tie WhatsApp or Signal to a Google Voice number, in which case the whole process can be done without a real (i.e. mobile carrier) phone number--you receive the SMS in Hangouts, type the code into WhatsApp/Signal, et voilà. Same caveat about one device at a time applies.

Do you actually use Signal? How well does it keep messages in synchronization if I were to use it on my phone and on my PC?

I do use Signal, quite a bit. But that's actually a feature I haven't used much.

If you do not need voice for the the iPad, use web.whatsapp.com in desktop site mode instead of the Whatsapp iOS app to avoid deactivating the phone. This works the same as using my Surface Book.

https://www.flyertalk.com/forum/undefinedPossible to do that with Signal?

https://www.flyertalk.com/forum/undefinedWith a Surface Book (running Windows) yes, with an iPad, no. Signal doesn't have a web client, only a desktop or mobile application.

Also worth noting is that WhatsApp's web client requires your phone to be connected to the internet--messages are still delivered to your phone and then passed to the web client. If your phone is off or doesn't have internet access, the web client doesn't work.

https://www.flyertalk.com/forum/undefinedJust note you need a connection on your phone, otherwise the web version doesn't work.

https://www.flyertalk.com/forum/undefinedI have never used Signal before, but I'm really interested in switching over. My main worry is that messages won't be in synchronization. iMessage and Skype had that issue for years, but the problem was solved once messages were stored in the cloud or something like that. I really don't want to switch to Signal if that problem exist. WhatsApp has been good as well. I just don't know how secured and usable it is going forward since it's owned by Facebook.

https://www.flyertalk.com/forum/undefinedI downloaded Signal onto my laptop just out of curiosity. Messages appear to arrive instantly on both devices and to update immediately on a device when brought back online. Unlike WhatsApp's web client, Signal's desktop application does not require your phone to be connected to the internet to send and receive messages on the desktop. The security key stays the same no matter what device you send from, so it looks like linking devices with Signal actually copies the private key.

I also noticed that it's possible to link an iPad in the same way as a desktop--the iOS app evidently acts differently on iPads than on phones. https://support.signal.org/hc/en-us/...Linked-Devices

You can't link a second phone or an Android tablet, though.

https://www.flyertalk.com/forum/undefinedThanks for the response. Are the messages in order though? Since you said Signal is linked to the phone number, if the phone is off, then how does your laptop receive the messages? Once your turn your phone back on, how does Signal rearrange the order of the messages so that they're in chronological order?

I'm not sure what you mean. The messages are sorted by time sent just like any other messaging app, so they stay in the same order. (cf. SMS, which are not time-stamped so they display in the order received, which isn't necessarily the order sent)

The server pushes the messages directly to linked devices, so although the phone is the 'master' device it doesn't need to be on for the server to talk to the 'slave' devices. (cf. WhatsApp, where the server pushes messages only to the phone and the phone relays them to the web client)

It's kind of hard to explain. When iMessage first came out even though it was time stamped, they weren't always in sync between my iPad and iPhone. I think you can probably search for it if you're really interested in the history of iMessage. Skype had that issue as well. So it was very annoying because the messages weren't in order so it was hard to follow along in the conversation unless I used my iPhone every time I used iMessage. Sounds like Signal doesn't have that problem, which is great! In your opinion, what does WhatsApp have over Signal at this point?