A home phone through a mobile network router?

[MeldrewsMate]

Some time ago I ditched my £30 a month phone and broadband deal, bought a ZTE286D router and fitted it with a £5 per month SIM from Smarty. I believe they use the O2 network. It worked, and still works, very well,
I noticed it had a (RJ11?) phone port so I connected my old home phone to it. To my surprise my first call (to my mobile phone) connected, and I was able to talk to myself, however the next call was disconnected soon after the calling phone started ringing. I can still, to this day, call this router's number from my mobile phone, just like calling any other mobile phone, however the phone doesn't ring and the call goes straight to voicemail, similar to what happens if that mobile phone is in a signal blackspot.

The simple questions, with hopefully simple answers, are as follows. My goal is to have the equivalent of a mobile phone on the hall table, but without the cost of a landline. I am not a heavy user of data; my current plan with Smarty is for (IIRC) twenty giggle-bytes per month.

1. Do I need VoIP credentials in order to use this router as the basis for a home phone?
2. Do I need to pay a monthly subscription? If so what do I ask for and who do I ask? Smarty? ZTE?

MM

 

[CountryFan]

I’m not au fait with much, but maybe, rather than use the old landline connection (probably why it was disconnected) maybe enable WiFi calling?

 

[jj4091]

I think that only enables mobile calls rather than to/from a landline number. Like you I'm not that genned up on that sort of thing so don't know a way round the problem