Fritzbox with third party VOIP

Do you think the zen supplied fritzbox can be used with a third party sip voip provider if you are not signed up to zens digital voice? Or is it locked or Zen or automatically overwritted by their settings? Thanks

Yes, no, no.
I have a Fritz 7530AX, a Gigaset N300A, and a few Gigaset DECT phones that are connected to the N300A.
Zen is my ISP.

The N300A supports:
1 landline connection, which connects to the FON port on the 7530AX, for Zen's DV service
1 Gigaset.net connection, which I don't use
6 SIP connections (all via one Ethernet connection to the 7530AX

I have three of the six services configured: Sipgate, FreeVoip, and Zen DV (unnecessary, as it's handled by the landline/FON connection). So I could simply use Sipgate and FreeVoip without subscribing to Zen DV.

I expect that I could use the Fritz box as a DECT base instead of the N300A, but I don't.

Edited by cjn (Fri 04-Aug-23 14:12:23)

I used the Fritzbox with Sipgate and a Dect system. No problems.

I've been using Andrews and Arnold VOIP on my FB7530 for the last two and a half years without any issues. Configuration is pretty straightforward. Just £1.44 per month and I kept my existing number, tech support are brilliant.

I'm glad to see this, and would be interested in any tips, as my attempts to do this using Andrews and Arnold VOIP on my FB7530 keep failing. My broadband - FTTP - is with Zen and very stable but I recently ported the number to Andrews & Arnold as Zen wanted to charge £7.50 a month for a line we rarely use for calls but is still useful to share with people happier to call on a landline.

I've followed the guidance on their site, and it works for while (from 8 minutes to 2 hours) but then fails: with the message; 'Registration of internet telephone number **** failed. Remote site reports reason for error 403'

The Andrews & Arnold helpdesk has been very patient but unable to sort this: they say it could be the router that's faulty, though the Zen service was fine for 2 years. The FrtizBox helpline suggest it's a provider issue as the connection works for a while. I asked Zen if they've any ideas - has the number ported properly? - but (unsurprisingly) they say they can't help.

Can anyone suggest what might be wrong? I've rebooted the router to no avail. I could do a factory reset but fear I'll mess up the home network in the process, despite recording all settings.

Edited by JAPrufrock (Wed 22-Oct-25 17:11:03)

In reply to a post by JAPrufrock:

Remote site reports reason for error 403

A sip error 403, like a HTTP error 403 indicates your request has been received by the server, but the server refuses to fulfil it.

That indicates a A&A problem or possibly a problem with your router. I would think your number has either ported or it has not, there is no halfway house. So when the phone is up, can you ring it? Do you get the correct display number when you ring elsewhere? And are you able to borrow an ATA or an internet phone and try the credentials? Could you try a sip client on your mobile phone?

In reply to a post by JAPrufrock:

I'm glad to see this, and would be interested in any tips, as my attempts to do this using Andrews and Arnold VOIP on my FB7530 keep failing. My broadband - FTTP - is with Zen and very stable but I recently ported the number to Andrews & Arnold as Zen wanted to charge £7.50 a month for a line we rarely use for calls but is still useful to share with people happier to call on a landline.

I've followed the guidance on their site, and it works for while (from 8 minutes to 2 hours) but then fails: with the message; 'Registration of internet telephone number **** failed. Remote site reports reason for error 403'

The Andrews & Arnold helpdesk has been very patient but unable to sort this: they say it could be the router that's faulty, though the Zen service was fine for 2 years. The FrtizBox helpline suggest it's a provider issue as the connection works for a while. I asked Zen if they've any ideas - has the number ported properly? - but (unsurprisingly) they say they can't help.

Can anyone suggest what might be wrong? I've rebooted the router to no avail. I could do a factory reset but fear I'll mess up the home network in the process, despite recording all settings.

I'm with A&A for VOIP. While I have never seen this error message I do sometimes get the account fail to register, but it's usually after there power's been off or the router's been rebooted. Disconnecting the ethernet from the ATA and plugging the cable back in fixes it. Not sure that helps but I thought I'd mention it.

Thanks for the reply:

So when the phone is up, can you ring it? Do you get the correct display number when you ring elsewhere?

Yes, it works as it should when it's live, showing the correct details on my mobile, for example (and in the FritzBox call records). I don't have access to an internet phone (the Fritzbox has paired with 4 DECT phones we already had - they work fine, as they did with Zen). I'll see if I can borrow a suitable phone or try using a SIP client on my phone, though I'm not sure if I can succeed at that

I am sucessfully using a FB7530AX f/w 8.20 , over Zen Fibre, with Sigate, voipfone and a specialist voip connection. Under telephone/line settings I have “ Use a random port for the SIP service of the FRITZ!Box to the SIP registrar” and “ Keep port sharing of the internet router enabled for telephony” both ticked, might be worth selecting, and rebooting FB, as a test?

In reply to a post by nickt:

I've been using Andrews and Arnold VOIP on my FB7530 for the last two and a half years without any issues. Configuration is pretty straightforward. Just £1.44 per month and I kept my existing number, tech support are brilliant.

Same here although only for 11 months in my case and with the AX version of the router.

Have you also noticed on your latest invoice, a not that the price is increasing to "£1.50+VAT from January 2026"?

£1.80 !!!

.