Some useful info for the OP in no particular order:
When you have signed up with Sipgate you can go to their web site,
click on Help, and it will take you (possibly after a few more clicks)
to a page that lists many types of ATAs and SIP-phones and gives you
their configs.
If you don't have a SIP-phone or ATA but want to try out the service
you can download X-Phone free of charge from their site which, when
you look into its config, you will find is already set up for your
account. You only need a mic/loudspeaker or a headset with boom mic
plugged into you PC to be able to receive calls or to make free calls
to other Sipgate users if you have not installed any credit. Just
ensure that X-Phone is not set to self-boot at PC startup or it will
completely cock up your system when you try to use the ATA.
Another VoIP software interface is Phonerlite which is also free and I
have found works very well.
A word of caution: if you use either X-Phone or Phonerlite avoid the
temptation to use a USB handset. VoIP often only uses one channel of
the stereo pair, and if the USB handset is configured (fixed) to work
on the other channel then you will have outgoing audio but no incoming
(the opposite of the Stun problem explained below.)
If you have a smartphone you can download CSIPSimple or SIPdroid
(Android) or Zoiper (iOS) and configure them so that you can use your
smartphone to make calls over wi-fi via Sipgate. You will then find
how little info is actually needed in the config to make VoIP work.
Just make sure it is stopped when you use your ATA or whatever.
A useful advantage of using such access however is that if, say, you
are on hols in Europe and have access to decent free wi-fi, you can
make calls from there at UK rates (roughly 1p/min to any UK number or
2p/min to most other countries) and it shows your UK number on CLI. I
say decent free wi-fi as many free providers - such as IME most
Mairie's offices in France - block everything bar Internet surfing as
the service is often provided by a telephone company (e.g. Orange
France) which means they loose revenue if you use VoIP. (They don't
even allow e-mail clients - you have no option but to use webmail!)
Having said that I have never found such blocking on any wi-fi in a
Tourist Information Office.
A useful advantage of ATAs is that they store the config in
non-volatile memory so it is never lost unless you press the reset
button.
Most ATAs are set by default for the US market, so you get US ring
cadences and US earpiece tones. A bit of Googling will bring up the
data you need to enter to get UK dial/engaged tones and UK ringing
cadences.
I suggested in an earlier post to get a SIP-phone but they have their
problems. Some of them (Grandstream excepted for instance) will not
let you change the ring cadences or earpiece tones so you end up with
the US version. If you have an ATA and connect a standard (BT-type) UK
phone to it then with the correct config you will get full UK-style
operation as if it were on a BT line.
You will not need to make any changes to your router config - the ATA
will just work once configured. I have a Sepura SPA2102 which has its
own router built in and is suggested to be fitted between you incoming
broadband modem and any router you use. Mine just sits on an a LAN
port of my router/switch. You may however have to play with turning
Stun on or off especially if you get one-way audio (usually incoming
works but outgoing does not.)
[Sepura was taken over by Linksys who in turn were taken over by
Cisco, but their management had the good sense to retain the existing
browser interfaces - which are very similar anyway. If you can find
any you can also use ex-Vonage ATAs but you need to unlock them first
and they are a little more idiosyncratic to set up.]
Finally there is an option to auto-insert dialling codes etc - it is
called preselection. With VoIP you MUST always dial the full UK number
including dialling code, but you can make the unit auto-insert the
dialling code if you dial only the number for a local call. This will
overcome any possibility of someone other than yourself making a local
call and not realising that the dialling code is necessary. It also
sets up 112/999 dialling to work correctly but note that you must
enter your details on the Sipgate web site so that if the emergency
service does a search against your number it will come up with your
address correctly.
Sipgate has dial-up testing: 10000 will confirm that you are
connected; 10005 will allow you to check audio both ways by using an
automatic answerphone-type system; 10020 will allow you to test DTMF
dialling from your keypad. Note that this may not work if you have set
up preselection depending on what that preselection contains.
To the OP, if you want a copy of the UK ringing cadences, UK earpice
tone settings, or preselection data contact me off group.