VoWiFi

> You don't need eUICC or anything of the sort to do roaming, which is just what he's describing. Even the behavior with the international prefix on numbers.

I don’t think the author made this claim at all. He just mentioned that he thinks that Google are using eUICC to make roaming on Google Fi cheaper than traditional roaming agreements. And he’s basing this on the fact that the dat connection can drop out for a little while as the phone roams internationally, presumably because it’s reprogramming the eUICC.

I would assume that if you’re running a service like GoogleFi, where the phone number isn’t associated with an actual phone network, then you can do international roaming cheaper because you just setup direct agreements with local telecoms to provide local data access, and then route the “shadow number” assigned to the SIM to a local Google endpoint. Thus you can create a setup where international roam is achieved by having local only carrier agreements, and doing clever call routing to local Google forwarding numbers, which Google then routes over its own network to the destination country, where a local Google endpoint then pushes the call back into the local telco network.

Doing this completely removes the need to have a traditional roaming agreement where carrier backhaul alien subscribes back to their home carrier, charging a hefty fee for the privilege. And instead replaces it all with local only call and data routing, with Google infrastructure providing international transit, and Google software masquerading the local subscriber identities, so GoogleFi customers don’t see the messy details underneath.

The lack of VoLTE early on was not quite as simple as missing software as there was, at the time, not really any agreed upon VoLTE architecture or implementation. IMS has existed since before LTE, but carriers have been very reticent to implement it because the choice to architect around existing internet protocols actually leads to a relatively high degree of complexity from the perspective of legacy telcos. For most of the early years of LTE, most carriers just didn't support VoLTE as an intentional business decision, to avoid the expense of deploying infrastructure. Those that did mostly deployed "lite" VoLTE stacks that were simpler and less capable than the IMS architecture, and this is the big issue that leads to the situation we still have today in some cases were given phone models are only capable of VoLTE with specific carriers, due to those carriers using a non-standard architecture.

Most LTE phones could do HSDPA+ during voice calls but some couldn't. I'm not sure why, it may have just been a simplifying decision by the vendors. This was more of an issue in the very early days of LTE, e.g. my hazy memory is that the HTC Thunderbolt completely dropped data during voice calls.

This is not related to LTE, just to roaming itself. In fact, even the manual of the first GSM phone I ever bought said as much (to store your numbers with the international prefix on the address book -- otherwise, they could fail to be matched while roaming).

Always storing contacts using the full international phone number is definitely the way to go. As someone who, at least before the pandemic, used to travel a fair amount this basically eliminates all issues and makes everything "just work" everywhere.

To be honest I'm surprised that phones doesn't do this automatically when you type in a local number.

I had a friend try VoIP on a dataplan a few years ago.

> The biggest problem I foresee is a lack of QoS,

Bingo. QoS for voice is about jitter and consistency of your stream.

> I'm hoping that best effort on a lower bandwidth stream will work alright.

Lets put it this way: you don't care if your webpage loads 0.2 seconds slower. But a few random 0.2 second delay in your conversations will make them utterly, and completely unintelligible. Low QoS is something data can afford because little "sprints" of high bandwidth is good for webpages and streaming video.

But "live", and "realtime" voice communications, the jitter is just too awful.

If no one else is on the cell-tower, you might be fine. But every now and then, you'll just get completely terrible phone calls that are unusable.

the biggest issue i ran into when trying voip with a cell phone is lack of functioning mms (and therefore also group sms). that ended up being the dealbreaker.

I've been using SIP on my Android phone for a couple of months now, and QoS hasn't been an issue at all. I'm using Voip.ms so I can have SMS and MMS. There's a SMS app but it doesn't support MMS; MMS messages are emailed to me and I just log on the Voip.ms portal and message there. I use Linphone as the client, and Strongswan for VPN.

The main difference VoLTE provides is preferential network access for voice calls. In times of congestion, voice calls will still work when data might not.

VoLTE calls also have a coverage advantage to them over data. Cellular networks have different handover settings for VoLTE (QCI 1/5) where the device can hold onto its RF longer while a call is ongoing and still allow the call to work using techniques like TTI bundling. The codecs used for VoLTE require very little bandwidth and thus can still operate in extremely poor conditions.

And if you're wondering why carriers don't just offer the same for data, it's because customers using data in cell-edge cases would be disappointed with the experience even with the extra handover settings and TTI bundling. That combined with the extra PHY resources being allocated to a situation where data just might not arrive 70% of the time makes it more worth it to allocate those resources to VoLTE specifically especially when they might be critical like in E911 scenarios.

I strongly recommend https://jmp.chat with their Cheogram app. Almost perfect mobile replacement.

Why would you ever care about area codes? At least if not for ancient carrier billing practices.

Hard disagree - it's actually pretty awful from a mobile user's perspective.

You dial a number that is +1 and looks like a normal 10 digit phone number.... and bam, you're paying $3/minute to call Canada (back when everyone charged more for Canada) or Bermuda that is still expensive I think on every carrier.

Everyone could use 10 digit dialing and have their own country codes still... it's silly that 19 countries are sitting behind +1 and that they might have a significant surcharge to call.

This behavior can make your internet on the phone really slow, especially if your SIMs home country is on the other end of the world.

But with 5G there is a mode for routing IP traffic directly to the internet during roaming, without sending it „home“ first. Let’s see if providers will implement that.

For Xiaomi, ##869434##, I'm not sure about other devices. Mine doesn't work, for some reason, but everyone else's works fine. I think my SIM is somehow misconfigured.