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  1. #1
    Join Date
    Sep 2005
    Feedback Score

    Lightbulb My experience with iOS 13, Dual SIM & IMS (IP Media Subsystem)

    I don't travel outside US too much, but I just spent a couple weeks in Colombia. I was suprised how non-intuitive it was to get Dual-SIM working like I wanted.

    When on Wi-Fi, I can send texts and make calls, browse web, etc.. via Verizon Wi-Fi calling and Messages using my Verizon number while not connected to Verizon's network. I just wanted a way to do this same thing, but on a local Colombian cellular provider instead of Wi-Fi

    Prior to arrival in Colombia I moved my Verizon physical SIM card to eSIM - this was quite challenging, several phone representatives on different days said it was impossible and refused to help me. On a whim I then tried talking to a chat representative and they completed the process with me in a matter of minutes! Not sure why chat rep was helpful quickly when multiple phone representatives wouldn't help.

    You also MUST setup Wi-Fi calling PRIOR to leaving country! When on Wi-Fi, provider status on my phone says "VZW Wi-Fi". Based on another post, once VZW was operating over Claro SIM card, it should say "VZW using Cellular Data".

    Once I got to Colombia, after an hour of reading macrumors, howard forums, reddit I think I pieced it together. I got a SIM card from Claro (a provider in Colombia) 1.8GB of data and unlimited text and calling for 30 days for $12 USD. I eventually found out that what I wanted to do would require a feature called IMS (IP Media Subsystem). My Verizon eSIM was called Primary, and my new Claro SIM I called Travel.

    In Cellular settings I did:

    Cellular Data - set to use Travel SIM
    Cellular Data - turn OFF "Allow Cellular Data Switching" so I ONLY use Travel SIM
    Cellular - I set Data Roaming OFF
    Default Voice Line - set to Primary (the Verizon eSIM) so that when I made calls it would be from US number by default - but using IMS.
    Both Cellular plans were marked ON

    But it still wasn't working! I didn't see "VZW using Cellular Data". It turned out a post I found on macrumors held the clue. I went into Settings > Cellular > Cellular Network for the Verizon eSIM and turn off Automatic Selection. Once the list of available Cellular networks appeared, I picked a small MVNO called Avantel. ONLY THEN did the magic "VZW using Cellular Data" appear (after a minute or two) - and my phone was acting as if it was on WiFi - but via my local Colombian SIM from Claro provider!

    My family had three phones setup this way, ZERO roaming charges from Verizon after a couple weeks in Colombia! And I was able to use my US verizon number for calling, iOS messages anywhere!

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    • It takes 1-2 MINUTES for "VZW using Cellular Data" to appear - don't be impatient
    • A few times I would see the Verizon line reporting "No Service" - I could wake it up by turning airplane mode on/off to reinitialize the Claro SIM and VZW using Cellular Data on eSIM.
    • The only people I texted were other iPhone users, so I don't know what happens when you text a non-iPhone user.
    • Cheaper data only plans were available and may have worked if i only wanted to use Wi-Fi calling, but I am glad I got a plan with voice minutes as I did use Travel SIM to call some local tours, restaurants, shops, etc..

    Hopefully this summary is useful to someone, but questions:

    1) Why is this so hard?
    2) Why did I have to manually set VZ eSIM to Avantel?
    3) Anything better I should have done?

    Post that mentioned manually switching provider:

    Original inspiration:
    Last edited by exxxcite; 01-05-2020 at 12:40 PM.

  2. #2
    Join Date
    Jun 2005
    Feedback Score
    I have used this system and it works well. The mystery is why carriers consider this a WiFi call, but I guess it's because of the data nature of the access from your voice line to the data line. You have discovered the correct settings by trial and error and that's quite an accomplishment! I am currently trying to figure out how to have two lines set up this way be able to communicate without any charges while roaming internationally. I don't think it's possible.

    I have found one drawback I believe, leaving your phone is this configuration. My iPhone 11Pro Max does not receive text messages on my primary voice line while it has a non roaming carrier selected. A small glitch, but I'm still hoping to find a workaround on that issue.

  3. #3
    Join Date
    Jun 2005
    Feedback Score
    I have read a lot and experimented a little and found that:

    1. "Data Roaming" and "Allow Data Switching" do not seem to have any effect on the use of this system, so setup becomes a little easier with no need to change those switches. So just turn off WiFi, manually switch your voice line to a "No Service" carrier and wait for the Control Center to display "Mobile Using Cellular Data" and it should be all set for free US calling.
    2. I will be testing a "3" UK 12Gb, 30 day, $20 sim (Amazon) in the future to see what tricks it can do. It appears that it should work with the IMS setup. The 3 sim should also work in Columbia according to the 71 country list provided. Also, one vendor told me via email that tethering is now included, but I'll wait and see if that holds up in the real world. It hasn't been changed in the listings.

  4. #4
    Join Date
    Jun 2005
    Feedback Score
    I called my iPhone 11 Pro Max from my home landline while both were in the US. With Data Roaming & Allow Data Switching both on, and then again with both off. The result were the same. If WiFi is turned off, the voice line has a manually chosen a "No Service" carrier such as in my case, Verizon or the First Responder-313 100 from the Network Selection, calls are recorded in my T-Mobile Account desktop and mobile apps as WiFi Calls.

    The setup is quite easy, and the only question for me that remains is, if the chosen "No Service" carrier is no longer accessible to the phone, will it then seek and register with another carrier automatically? I doubt it, but I'll need to see what happens if that occurs.

    Edited to add: I just ordered a Red Pocket sim running Verizon service. On Ebay they are $60 for a year of 500Mb, 100 Minutes, 100 Texts per month. That's more service than I ever used on Xfinity Mobile, also a VZ carrier MVNO. I'll report the function of this service also as the data line for simulated WiFi testing.
    Last edited by daleraver; 01-11-2020 at 10:56 AM.

  5. #5
    Join Date
    Jun 2005
    Feedback Score
    I received my Red Pocket sim yesterday and set it up in a few minutes. It works well and the on line account manager is decent. Actually easier to use than T-Mobiles, but it doesn't have as many options. There is no Red Pocket app however. The RP line cannot be carrier switched. The Network Selection will not turn off from Automatic. It therefore must be the data line (At Least In The US), with my T-Mobile line used for the voice service.

    With my T-Mobile voice line on a No Service carrier, calls do show on my plan app as WiFi. I ran a test for a little over a minute, and the data used was around 2Mb. I've heard that voice calls use around 4Kb a second, and this short test seems to support that.

    This workaround function is a real game changer for frequent travelers in my opinion. It's possible to leave your phone set to make and receive calls from the US in any included roaming country without the need for connecting to WiFi. It's convenient & thrifty and the voice quality is good. I wonder if the carriers will care enough to try and monetize it? It doesn't cost them anything, and you are just using someone else's data typically. In my case it will either be Airalo or 3 UK prepaid roaming data.

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