VOIP working well. Two calls at once!

Thanks for all the help on this very useful forum. I took the plunge in January, and switched to VOIP with A&A. Equipment: Gigaset N300A and C570HX handset from Ligo. The number transfer worked perfectly, and it was almost like POTS! Very clear voice, lots of nice features, answerphone works well..
So recently I bought a second handset (a C575HX) for the study. I registered it to the N300 All working fine. When there's an incoming call, both handsets ring, and you can answer on either. You can't listen in on the ongoing conversation from the second handset though, as you could with the old analogue DECT phones. Is there a way to do that?

But the main reason for this post is to say that much to my surprise (and hereby revealing my newbie status on VOIP) I discovered that while my wife was talking on the kitchen handset, the second handset (in the study) rang, I answered, and found myself having an entirely separate conversation with perfect sound. Since this happened I've done some more tests and find both phones seem to work independently. Two calls can occur at the same time. I can call out from the second handset when the first is in use. So we appear to have what are effectively two separate lines, both with the same number, one per handset. All via a single A&A account. I hadn't expected this, and hadn't seen anywhere that VOIP would work this way. Of course, there's no reason why not! Did I miss that this would happen? If I buy a third handset, can I have three calls simultaneously?
All very interesting. One thing I never did work out is whether there is a ringback (when engaged) feature. Any way to do this?

In reply to a post by WBJB:

If I buy a third handset, can I have three calls simultaneously?

That depends on how many simultaneous calls the N300A and your provider support

Yes you can listen in on another call I believe, according to page 43 of the phones manual.

I believe you can have 3 parallel calls on the n300

1 analog and 2 sip.

the ip510 and ip610 offer more (ip 610 pro offer 8 handsets and 8 calls per base station)

Yes, VoIP can do this depending on whether your provider supports it (most do, they want you using the service as much as possible) and whether you're keeping within the simultaneous call limits of your DECT base, which is a limitation that exists separately to any VoIP-specific one.

If you take BTs Digital Voice service you can change the operation mode of the DECT handsets to either work like an old set connected to an analogue line, where picking any phone up would join you to the in-progress call, or to function like a VoIP set would by default where you have to transfer calls if you'd like to move them between handsets. I think it was spelled out in the supplied literature as well as by default it worked in the VoIP style but I can't remember for sure.

LISTENING IN:
Thanks. I have (a) a Gigaset CX570HX and (b) a CX575HX. The manual that I have is for the CX570. It covers this on page 35. The manual and the phone don't match. The manual says you go to settings > Telephony -> Connections. But there is no connections option. There is both a Send-connections and Rec.Connections options. Neither of these has an option to permit or prevent internal listening in. I believe I am at the latest firmware levels on the N300 and the phones. The CX575 is exactly the same.

The manual I have is dated 2017 - but it is the phone that seems to lack the option.

Edited by WBJB (Sat 24-Aug-24 14:00:17)

It would be a setting on the base, I can't see anything in the N300 manual suggesting that it works in this way.

On my N300A, Telephony / Audio shows an option "Allow 1 VoIP call only" --- Yes / No
This should do something useful.

same for the n510

I found the description and it refers to it being there to save bandwidth, not that it treats all the phones as a single device. I guess it's just going to have to be a bit of trial and error if that's the behaviour that someone wants.