Obviously some sort of VOIP app is required for that, to run on one's mobile phone.
Also a means of "connecting" the local network (wifi/ethernet) call to the telephone system.
I know one can sign up with a VOIP provider and get a whole VOIP solution for one's business (usually crap quality, from what I hear all day at work when these people phone me) but there must be a simpler solution... for example is there a box which has wifi or ethernet one end, and which plugs into your home phone system as a fake extension phone?
Skype?
Peter,
Your post talks about putting the phone as an extension in your home, but the title talks about making calls over wifi from your mobile phone.
Both are possible, and relatively trivial.
In either case you'll need a VOIP provider. These are two a penny. If you only want to make outgoing calls, then you can find some pay as you go services. If you want an incoming number then you'll need some sort of payment plan. You can get incoming numbes for various different countries.
If you Google for VOIP you'll find loads of them. I use a company called www.freespeech.ie as I don't need an incoming number, and they have a committment free pay as you go plan including some free minutes daily to certain destinations.
I'm not saying that they are the best, or even good. But the amounts are so trivial, that it isn't worth the time shopping around.
Once you have sorted a VOIP account, things are really simple.
For your mobile phone you just need a VOIP app, and input the details for the server and account from your VOIP provider. On Android I use a free app called cSipSimple. I've forgotten the name of the free app I used on my iPad, but can get it for you if you wish. On my PC I use a free program called Counterpath X-Lite.
I don't use Symbian, so have no idea about apps for your Nokia, but I'm sure that there are some available.
To connect a physical phone to your home network you can use a little box that does the work of the app. I used a cheap box called Linksys PAP2 that I bought from EBay. It connects by ethernet cable to your home network and the phone plugs into it.
Having said all that, the quality of the calls can be variable. From a really good network, wired connection, they can be fine. From a slow flaky wifi connection you won't be able to make a proper call.
Then there is everything in between. It can be handy when away and connected to a hotel wifi network if the network is good.
dp
Apologies for ambiguity 
I think the reason I would like to use the mobile phone at home, despite having the land line (which is what any sensible person would use) is that I have the contacts database on the mobile phone.
There ought to be a way to make an outgoing call via one's land line, using the mobile phone's wifi connection. I can't see the need for a VOIP provider because, outside your house, it will be a land-line call.
IOW, the mobile phone works as an extension phone on the home PBX, so one could answer incoming calls with it too.
Some years ago, IIRC, Ericsson made a GSM phone which also had DECT, but it failed because none of the cellular networks would touch it because it was obvious that whenever the owner was at home, he would be making land-line calls with it (via DECT). What I am after is the same thing, but over wifi.
Ah so you're looking to make a regular PSTN call over your home land line account, using your mobile phone.
Sorry...can't help with that.
I actually don't care how the outgoing call is routed, so long as my phone # is presented as CLID.
Skype gives you that, I believe, if you purchase the "London" number. But Skype calls are really crap quality.
You can do it, but I would wager it's more trouble than it's worth. You need a device at home that on one side acts as a SIP server and on the other talks to the PSTN (i.e. your regular land line socket on the wall). Technically that's an FXO device. We've done it in the past using a little PC running Asterisk, with a PCI (standard PC expansion card) FXO board. But it's a pain to set up. It's easier with a package like FreePBX. Still, that's a lot of hardware for doing something so simple. This might do it, but I've never tried and the documentation isn't very clear - a good thorough read of it might yield the evidence you need.
Then it's simply a matter of a SIP client on your phone - as dublinpilot, I don't know about Symbian but I imagine there is one.
But as I say, this is a lot of trouble to save the need to transcribe the number from your mobile phone address book in to the phone on your desk. And when that's too much trouble personally I just use my mobile for making the call in the first place.
I actually don't care how the outgoing call is routed, so long as my phone # is presented as CLID.
A VoIP gateway service like this will allow you to present your CLID, provided you can certify that you "own" it. For the record, there is nothing wrong with VoIP quality (after all, the vast majority of big businesses use it), but if you're running it off of a consumer-grade ADSL line whilst others in the house are downloading videos and playing Mincraft then the quality will vary.
Thanks for the pointers David.
That's probably why nobody I know does it
We have near-zero signal here in the countryside, and zero inside the building, hence... in fact I even bought one of those illegal GSM repeaters for £200, which sort-of works (in the loft) but it needs a much better "output" antenna.
Peter,
I have two VOIP accounts set up through my Router; I could use the box above if the facility was not in the router. My mobile phone (HTC) allows me to enter the VOIP account details and when it is connected to the router by WiFi I can make and receive calls to the VOIP numbers. Works through other peoples WiFi, is a damn sight cheaper than using the mobile and works anywhere in the World. VOIP account is PAYG with no fixed costs.
