Tech: Why can't 2or3 SimCards use same number?

Subject: Tech: Why can't 2or3 SimCards use same number?
From: punkfolkrocker
Date: 22 May 18 - 11:25 AM

Anyone understand why mobile phone operators can't let us use the same account and phone number on more than one sim Card...??

I have an account with a mobile operator that I am reasonably satisfied with,
and 3 smart phones still in good working order, each more useful than the others for a specific purpose.

It would be very useful If we could have a Sim Card in more than one phone tied to the same phone number and account.
Surely the big mobile providers could adopt technology that effectively records data usage over over a reasonable amount of Sim Cards
within the same account...???

It's such a pain having to use different pay as you go sim cards and numbers, alongside my main monthly account.
and not practical to keep swapping the card between phones...

It can't be that difficult for the phone companies to sort out this very practical solution...????

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: punkfolkrocker
Date: 22 May 18 - 11:29 AM

Obviously I'd only need to use one mobile phone at a time.

I wouldn't expect the full flexibility of home landline DECT systems of multiple handsets on the same phone number.

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: Kenny B (inactive)
Date: 22 May 18 - 11:49 AM

Each sim-card has a unique identity to allow it to be identified and called at the location its logged on at. If you had more than one handset on the same number which one would it call? , it can only call one sim-card at a time.... does that help to explain what happens … but not to solve your problem.
You could use call transfer on "no reply" but that is costly

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: punkfolkrocker
Date: 22 May 18 - 12:24 PM

Kenny - that's a fair enough explanation for the system as was and as is..

But for the future, It surely wouldn't be that difficult for tech developers to modify the Sim system,
and update relevant apps...???

ie.. a manual option within the app to switch over and select which phone you intend using next,
disabling the others from the system, until required to be selected for use...

I don't hold out hopes, but it would definitely be an improvement..

At the moment I have 2 sims and numbers in use,
and soon to choose another pay as you go for a phone
[the wife's latest cast off]
that would be better in use, than gathering dust...


Wives and police can get a bit suspicious of blokes with several mobile phone numbers...

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: Kenny B (inactive)
Date: 22 May 18 - 01:06 PM

I think in the short term you could use call forwarding to the phone you were going to use at that particular time.
I have roughly 1400 song words in my phone and mirror my files into my car mobile just to be sure to be sure …. different size screens for reading

I have never heard of anyone wanting the same number on two or more phones although some phones can have two numbers/sim cards.

If there was a demand for it im sure the phone companies would be working on it although security probs could put them off if anyone other than the News of the World was listening to your conversations as well as looking at your texts :<) Smiley

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: Joe Offer
Date: 22 May 18 - 01:13 PM

I would like to have a mobile setup similar to the DECT system we have in the house and use less and less. We are paying ATT $230 a month for DSL, landline, and 3 mobile phones. There has to be a better way.
Moved this to the non-music section because it's non-music tech.
Joe

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: punkfolkrocker
Date: 22 May 18 - 01:14 PM

I think the phone industry prefers a scenario of new models every year,
and 'old' perfectly good phones going into landfill..

ok.. they are making some token gestures to recycling...

But the basic principle I propose, is already in use by Amazon Prime
for customers with multiple Prime/Fire devices..

and software developers who permit installation on more than one computer at a time,
but require one to be uninstalled if adding an extra device over the limit..

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: DaveRo
Date: 22 May 18 - 01:19 PM

It's available - but using Voice over IP (VoIP) and the data transmission facility of your mobile rather than traditional voice calls.

VoLTE is a method of voice calling over a mobile data connection. If you google something like 'volte single number multiple devices' you'll find several operators offering a single number on several devices - or planning too.

This explains how it works:
Ericsson: Multi-SIM: One Number, Multiple Devices

It could also be done using an app, in the same way that message sent to an apple or google account is received on all devices. You'd just respond to an alert and start a VoIP call. I don't know if anyone offers such an app - I expect so.

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: FreddyHeadey
Date: 22 May 18 - 01:52 PM

t mobile .com @ $10 /month
app for smartphones I think

https://www.t-mobile.com/offers/t-mobile-digits

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: DMcG
Date: 22 May 18 - 02:11 PM

I sort of understand why, because I work with people who specialise in this stuff. And in fact it happens illegally in parts of the world: people clone SIM cards so they have the same IMSI and then rely on being in sufficiently different parts of the network that there is no conflict between masts. But to do it legally would require different international standards to those that define how LTE etc work. In essence, though, you are talking about the network holding different phone number- imsi mappings, rather than necessarily any change in the phone. As I understand it - which isn't that much! - doing this using voice over IP works because every device has a separate IP anyway and that is the primary routing mechanism.

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: punkfolkrocker
Date: 22 May 18 - 03:09 PM

If I was a member of a consumer tech research opinion panel
I'd ask..

Why can't each Sim card still have it's own unique security ID,
whilst being enabled to intelligently share the same mobile phone no with a reasonable number of other Sims
on the same account and network...???

Even existing technology could probably make this do-able for next generation phone systems...

Imagine ordering, for example, a 3 pack of Sims with the same phone number...

At it's simplest each Sim could auto connect and disconnect from the network
as it's handset was switched on and off...

With a warning notification telling the user if they forgetfully had more than one phone actively trying to connect..

ie.. neither would be connected until all but one was switched off...????

I'm certain it could be done easily, and effectively, at minimal or no extra cost to consumers...

I'd immediately buy in...

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: DaveRo
Date: 22 May 18 - 05:27 PM

Yes, it could have been done with 2nd and 3rd generation mobiles. Maybe some operators did offer it.

The network control computers would need to identify which SIM(s) associated with a called number are active and which one(s) to ring - based on their recent use or movement say. The first one answered could connect, or several could join the same call. Not insuperable to implement, but not simple either - I think roaming might be problematic.

But VoLTE and VoIP are current technology, so I don't see anyone retrofitting it to UTMS or GSM.

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: Mr Red
Date: 23 May 18 - 03:55 AM

You would have to have (new) software in place that tried each other network (and piggyback networks) in turn while the (new) software at each network tried to locate a responding phone. Which might be out of range of a mast.

That would require cooperation between networks that prefer to compete. For a very small market (IMNSHO). Only legislation would make networks cooperate.

And the legislature want simplicity for fighting crime. And think of drivers causing accidents while on the phone☎. The police would check the phone and find no recent calls on the decoy phone!

The simple answer is: that anything is possible, but a nightmare to get working without hidden caveats. And software bugs. And loopholes. And .....


☎ FWIW US research put the cause of road accidents where a phone call is implicated at 70-80% due to the call, and the rest due to holding the phone. People visualise the person at the other end. Thus leaving less of the visual cortex for the job of controlling the dangerous weapon they have in their hands!

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: DaveRo
Date: 23 May 18 - 05:15 AM

I wrote: Maybe some operators did offer it.

A bit of googling on howardforums reveals that singtel had a facility by 2010 called 'multisim' which allowed up to 4 SIMs with the same number. It was discontinued in 2017 in favour of something else (presumably IP based).

As I suspected, there were restrictions on roaming (because the home operator only knows which other operator last saw its SIM, not whether it's still there, or active, or moving.

Apparantly it's a facility allowed for in GSM but rarely implemented.

(UTMS in my last post should have been UMTS)

Subject: RE: Tech: Why can't 2or3 SimCards use same number?
From: Ross Campbell
Date: 25 May 18 - 03:10 PM

A friend in Switzerland has a land-line and mobile with the same number for the last six digits. Seems like a very handy arrangement, but not a facility I've seen anywhere else. Why can't mobile services offer this in UK?
Ross