What I keep finding is that often there is zero signal showing on the phone (Samsung S6) and when I try to send the message I see some WIFI activity, and then the message appears sent. But there were no signal bars showing at any time…
I know of the caveats with sending texts over the internet e.g.
The Apple I-message system does it but only if both devices are online on the internet, you have to tell your phone what its number is, and Apple maintain the phone # – phone ID association on their servers. And it comes with some issues (have to manually dis-associate if the phone is lost etc).
I have found cryptic references to a thing called Google Voice as being capable of SMS over WIFI but I have not ever supplied google with my mobile number, and in this case the recipient is able to reply to me normally.
Spooky!
Of course it could be that the phone is simply lying about having really zero signal. I am pretty sure it sometimes does that with LTE (4G) connectivity, but LTE has the same issues as WIFI – it is just “internet”. Or is there SMS routing taking place over 3G/4G? That would be possible because obviously the cellular network does have your phone #.
There is also a thing called “wireless calling” which EE are advertising now, Vodafone will have it soon, but this is available only on phones which were bought in their shops on their contracts 
One can get it on a SIM-free phone by flashing the phone with that firmware, but that’s the last thing I want to do 
Anyway, VOIP gives you exactly that, for outgoing calls or texts only (text delivery is usually pretty sporadic though).
(BTW most Android SMS apps abandon the transmission of a message if there is no signal showing at the moment you press Send. I found one eventually which just waits for a signal. Irritating if you like in the UK countryside, and incredibly stupid functionality. One of the first reasons for flashing a Nokia was to get infinite SMS retries…).
With EE (and presumably others now) on handsets like the Galaxy S5/6 there is an option under Calls called “Calls over wifi” or something. This means that when the mobile signal is lost and there is a wifi signal the phones keeps working transparently with the calls and SMSs being sent over the wifi signal. You get a new icon appear at the top of the screen which looks like an upside down phone with a wifi icon above it when it is enabled.
Unfortunately this service doesn’t work when roaming (how it knows you are roaming I don’t know if there is no phone signal) but works great in the UK in places with no cell signal but wifi signal.
I have noticed though that when you call someone and it is going over wifi you number doesn’t always show up on their caller ID.
PS you can receive calls and txt messages too as normal.
No signal bars is a weak signal. A circle worth a line through it is no signal.
Three have a similar app called ‘inTouch’ which allows SMS and calls over wifi but in the UK only. I wonder if routing through a VPN or something would be enough to bypass this though…
Peter wrote:
But there were no signal bars showing at any time
The bars are an average over time. So it’s conceivable that you might have a signal at the moment you press send, but not show any signal bars. That doesn’t explain why you’d see wifi activity at the same time though. MMS uses a data connection of course, but I doubt it’s using that.
I understand that text messages with certain emoticons (basically any type beyond the basic ones e.g. :) ;) :-) :P and a few others) are sent as MMS and therefore sent over GPRS/3G/4G. I’ve noticed that the modern phones have a massive range of emoticons – here is just a tiny selection
and I don’t think they get sent as a “character”, not even a 16-bit one.
It could be that the phone falls over to mobile data (and sends the message via MMS) if it can get LTE but not GSM. Not sure however if it is possible to have LTE without GSM…
The iPhone gets its number from the SIM card, nothing to configure manually. I swap the SIM in mine when traveling between the US and the UK and the phone always knows which number is active.
The number is not in the SIM card. It is associated with the SIM ID by the network.
You must have at some stage entered it in, for each SIM card, maybe in some context like in your owner’s details and then it would get picked up for any SIM card, as soon as the phone calls up Apple, which it does at least every day.
I understand that text messages with certain emoticons (basically any type beyond the basic ones e.g. :) ;) :-) :P and a few others) are sent as MMS
Not on an iPhone at least. I just tried it. No data connection whatsoever (GSM-based or wifi), yet still able to send a full range of emoticons, including ones that have only been developed very recently, e.g. people with different skin tones. Apparently SMS uses UTF16. That does mean it won’t be able to send everything – some characters these days use four bytes.
