In message 
          Chris Green  wrote:

> Are there any simple 3G/4G add-ons for a Pi that will allow it to power up
> into a mode where it has the ability to be connected to via the mobile data
> connection?
>
> I want a system that I can connect to from my home desktop/laptop on
> demand.
>
> Sort of 'thinking out loud' about this:-
>
>    I suppose a USB 3G/4G dongle could provide the hardware required
>    to make a mobile connection to the PI, recommendations?
>
>    It has to 'connect on demand' dialling *to* the Pi, it can't keep
>    the line open all the time, very expensive!
>
>    So, is there software for Linux (and thus for the Pi) which will
>    handle incoming calls to allow ssh login?
>
>    How does one manage the other end?  Is there Linux desktop
>    software to allow one to dial up a remote system and then squirt
>    ssh down the connection?
>
> Any/all ideas would be very welcome.
>
> I'm happy with fairly low-level stuff, I am a retired software engineer,
> grew up with Unix (solaris) command line and I'm also quite into home-build
> electronics projects.

It seems very much to me that this depends on whether the Pi can have
a fixed IP address, or be behind a router that supports Dynamic DNS.
If either of those is true, you can ssh to it easily.

If you have no idea of its IP address, then it gets somewhat harder.

Tell us a bit more about the Pi's connectivity, and we may be able to
help you more.

David

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