Google's Project Fi does work in iPhones (if they're unlocked) when you travel internationally. It's not quite as effective as using a Nexus (now Pixel) device (they switch between carriers more effectively, they're designed to), but it does work. Can get you down to one SIM if you don't mind not having a local-to-the-country phone number.
EDIT: To qualify this, it's more useful if your primary country is the US.
> if you don't mind not having a local-to-the-country phone number
This is actually one of my big pain points with SIM-juggling while travelling. iMessage would work great, except for the fact that Apple unregisters your US number and registers your new SIM number in its place. Which makes total sense on a technical level, but is irritating in practise.
"This is actually one of my big pain points with SIM-juggling while travelling. iMessage would work great, except for the fact that Apple unregisters your US number and registers your new SIM number in its place."
I use twilio for this. I picked a nice, easy to remember twilio number in my preferred area code and I inserted a very simple "twiml bin" that will forward that number to a number of my choosing.
So now, I can use any old SIM I like (at home or while traveling) and I just need to edit the call forward rule.
I am also able to do nice things like not have voicemail. With US carriers, you can either have voicemail, or have a confusing message about "customer has not yet set up voicemail" ... instead, my number simply rings forever...
One tip: If you want to call people with the caller-ID of your twilio number, regardless of your SIM number, you need to use a VOIP dialer (there are excellent ones) and set up a SIP endpoint at twilio (five minutes). Your outbound calls will go through the SIP endpoint and a line of code or two sets your caller ID to your twilio number.
My slightly expensive hack-around is to have a second travel iPhone, and tether my primary phone to that when I travel.
I used to swap SIM cards around so that my primary SIM ended up in my travel phone, and my region-specific SIM ended up in my primary phone, but ultimately that became more hassle than it was worth, and tethering was a less painful solution with the prevalence of wifi everywhere in most places I visit.
I wonder if anyone on HN can recommend a cheap-ish tethering device? That had occurred to me before - some little hotspot thing I can throw a SIM card into. Maybe annoying to keep charged, though.
I was thinking "hotspot without phone", if only for a possible battery benefit. But realistically, Android phones are already so cheap that they're probably the best option.
Yeah, these are extremely common in the military. You get a "puck" (hotspot box), install a SIM for Kuwait or Iraq or wherever, and then you've got Wi-Fi Calling, iMessage, etc. on your U.S. phone and U.S. number.
I have a TP-Link M7350 from my last deployment. Don't think it works on Verizon bands in the U.S. though.
You just plug a sim card to it and it creates a wifi network that you can connect your devices. It also has a usb cable so that you can plug it to a computer to charge it, even though the battery lasts long enough.
I have a Huawei E5573 (a lot of carriers give them out free with data contracts), however I'd just recommend using an old phone. The battery lasts for around 2 hours when tethered, and the signal is no better than a phone (although you can connect an external antenna).
I considered both the Android option and the mobile hotspot option, neither effectively solved the problem of using the local SIM for voice calls and providing access to my full contact database (which is currently stored in iCloud).
If you have no need for voice calls, or your address book, or have your address book stored on a more cross platform friendly service, then either of these solutions will work for you!
Do you keep SIM cards after each trip? Seems like a hassle having 15 phone numbers to track, unless you're fully committed to being on Google Voice or something similar. Why not just pick up a new SIM each time you travel? Or just pay for an international plan if you travel frequently?
EDIT: To qualify this, it's more useful if your primary country is the US.