UKC

the more i ponder this it seems to me that the ideal solution to my phone needs would  be solved by this. one : mid range smart phone (iphone 7 say) for normal phone tasks, internet, email , music . two :  small , very rugged / tough, possibly water proof or as close as possible ( not full immersion but wont throw a hissy fit if left in the top of rucsack that gets damp or in a jacket pocket likewise,  long battery life, no smart features , just calls and texts .  it would be very easy to swap between the two.   does anybody have this set up ?

In reply to mike123:

Confusingly, a quick Google (I am not expert in this at all but your query interested me) suggests "probably not in the UK". It looks like "multi SIM" (more than one SIM card running off the same number/contract) is quite feasible in the USA but I don't see much about it in the UK (it doesn't help that multi-SIM also seems to mean a SIM card that can have different amounts of surrounding plastic popped away from it so it can go in the different sizes of SIM holders!). 
But I have a feeling that you are out of luck  

In reply to mike123:

Dumb phone with PAYG SIM/number and then set iphone to divert calls.
You may get a better deal as an add on to your current SIM contract.

Incoming calls are to iphone - they don't know you are on dumb phone.

Outgoing calls/texts will be from dumb phone's number. Possible confusion.

In reply to elsewhere:

Aye it seems that that is the "easiest" way to do it, assuming that there are not weird obstacles/restrictions to setting call forwarding. Can you set text forwarding? That could get (mildly) confusing for the person at the other end if they send a text to one number and receive a reply from another.

In reply to Blue Straggler:

thanks both, i should have said i used to do just that when phones got silly big.  i used to use a tiny nokia ( i still miss that phone !) as my hill / outdoors phone .  i cant remember for sure but i may have drowned it.  its just a faf remembering to switch. 

In reply to Blue Straggler:

Text forwarding - I don't have iDevices but google says yes.

https://support.apple.com/en-gb/HT208386

The outgoing calls/sms are still going to be from dumb phone.

In reply to mike123:

It is possible to have two devices running off one contract/number as that’s how the Apple Watch works alongside the iPhone. Whether a carrier will do it for two phones I’ve no idea but it’s technically possible. 

In reply to mike123:

Nokia 700, about the size of a thick bank card?
It's what I've got and want a 2nd SIM so I can use it for rugged manly outdoor stuff

In reply to mike123:

I just have a cheap smartish phone and a waterproof document pouch. Place 1 inside the other et voilà - weatherproof phone 😀

In reply to mike123:

Would it be simpler to just get a waterproof smartphone?

In reply to Andy Hardy and girlymonkey:

OP likes small and with maximised battery life.

In reply to Blue Straggler:

Mine is a Motorola G9 ~ 3 days worth of usable battery

In reply to mike123:

Is it not quite easy to jsut switch your sim card between the two phones?

Seems like an obvious answer to me, but the fact that no one else has mentioned it makes me think I'm missing something?

In reply to mountain.martin:

Shouldn't be an issue, but a bit of a faff with a little pointy tool, especially if you have to remove each phone from a case to the swap over.

AFAIK you can't have one number registered to two SIM cards in the UK. Not sure why not though. Mobile networks are pretty complicated. As I understand it, (I may well be wrong), your phone is constantly registering the IMEI number with local masts. The IMEI number and associated mobile phone mast(s) are then added to a database on a server somewhere, which is constantly being updated as you move around. If someone dials your mobile number their phone connects to a server, which looks up the IMEI number associated with that phone number, then looks at the database to see which masts have a signal registered to that IMEI number, then tries to find a free channel on the mast to connect the call. As you talk, all this stuff is constantly running in the background and keeping you connected. It's probably a lot of faff for the network provider, and maybe there are security implications in there somewhere?

In reply to Ridge:

A very basic one is what happens if you lose one handset and some "bad person" finds and easily unlocks it and can pretend to be you...

In reply to Blue Straggler:

Thats no different to losing a single phone. It probably undermines two factor authentication, and would probably make call tracing more difficult.

In reply to Ridge:

The slight difference is that you lose the "second" (less used) phone, you may take longer to notice that it's missing. 

In reply to mountain.martin:

Not a deal breaker but the sim cards are likely to be different sizes so OP would have to hang onto those little adapter pieces.

In reply to mike123:

Waterproof pouch does it for me:  youtube.com/watch?v=-AvSMgF4-rM&

In reply to elsewhere:

That'll be based on Apple's proprietary messaging system.  In my experience a regular GSM divert doesn't divert texts.