Transfer Call Between 2 DP720 connected to 2 different DP750


Hi, for our company we buy 2 Base DP750 and 10 Cordless DP720, so in every office there is a cordless.
Now i want to know if is possible to transfer a call between 2 cordless registered on 2 different DP750 base because i don’t find a way to do it.

Thanks a lot and sorry for my english.


Presumably each handset has a different extension number so you simply transfer the call to another extension


Sorry but i don’t really understand what you mean.
I create 2 profile in my Fritzbox for any base DP750 and then i connect 5 DP720 cordless to any DP750. The line in incoming and outcoming work good, all the phones rings when a call is incoming, but when someone answer and need to transfer the call to a DP720 connected not on the same DP750 is not possible.


I assume that all the phones are essentially set to be the same as they all ring at the same time on an incoming call, correct?

If so, then no, you will not be able to transfer calls between handsets as:

  1. The DP750 are endpoints and know nothing about each other. The Fritzbox would have to handle the negotiation and transfer between the handsets. The request would come from one of the handsets to the Fritzbox and then the Fritzbox would need to find the requested extension and arrange via an INVITE the transfer to the extension that is to accept the transfer.
  2. The handsets would normally be set such that each one would have a unique number/extension assigned to it. In this manner and with a SIP server of some type to negotiate the transfer a call could come in and be answered by extension 100 and then extension 100 could take the call and then transfer same to any other extension - 101, 102, 103, etc.

You might be able to do an direct IP call/transfer, but I am uncertain about it and it is not very elegant as it requires quite a bit of manipulation and that is assuming the handsets will support the function.


The DP720, like any IP phone, does not transfer itself, but according to the instructions of the VoIP server to which it is registered.
In your case the voip server is the Frtizbox, so you have to look at the Frtizbox instructions for transferring calls from one extension to another.


Probably i do something wrong, but i don’t understand which number insert when i transfer the call from a 720 to the other.
In my Fritzbox i create an account connected to the inbound number and i assigned the intern **620 to the 750 and another intern **621 to the other 750, but like this all the 5 cordless have the same intern, which is the intern of any single 720?


the advice is to create a single extension for each laptop and so with the instructions of the Fritzbox independently you will manage each extension


Hi Chris,
Below is an example that i assign 5 different SIP account (Extension) for 5 handsets (cordless in your statement), please notice the HS Mode, which is for incoming ring mode, so you want calls to 3501 only ring HS1, and calls to 3502 only ring HS2, etc. If you want an incoming call can ring all handsets, you can configure it to Parallel mode, which in my example is account 3510, notice you will assign it to all handsets at the line settings.

To transfer an call:
So when your handset 1 is in a call and want to transfer to HS 5, you can use “Option” -> “Transfer” -> then enter the HS5 accounts (3505 in my example). You can also transfer an call on 3510 to 3505 without issue.

You can change the 35xx account to anyone you are using, 620, 621, … 630 …, it does not matter as long as your Fritzbox has that account avaialable.


First of all thanks for all the answer, this is really a nice support, i hope that in the end i can use these cordless because i like the company like your that are useful for the customer.

Your idea to do the things are really smart but i cannot do.

The value “Sip user ID” and “Authenticate ID” must have the same value, true?

The problem is that when i create the account for the IP phone on my Fritzbox Fon WLAN 7390, the username must be minimun 8 character , i cannot create a user like “3501” or “3502”, so i cannot insert for the SIP User ID.


Also i can call directly another cordless typing **620 or **621, but when for an incoming call i cannot transfer using **620 or **621, sounds like it busy but don’t write “line busy”.

And also if i do a conference i can contact the other cordless with **621 or **620 but we can talk only in 3 if i want that hte cordless that i contact and the incoming call stay alone is impossible, if i close the call gos down for all and i cannot transfer in not others ways


Ok, i found the solution.

Thanks a lot to all the people that use their time to help me.


Shawn -

Well, I’ll be. Good to know. Thanks,


In general, from the SIP client perspective, no. In fact some people like having the Auth ID different than the UserID or extension number.


drostoker is right, the SIP User ID don’t have to be the same as Authenticate ID.
SIP Account usually have below IDs:

  • SIP User ID is the identity for the PBX to reorganize every user.
  • SIP Authenticate ID is the ID that used for registration. which is usually bind with a password.

Be aware the some SIP account have an:

  • SIP Caller ID, which is used for dialing or receiving incoming calls.

For an extreme example:
SIP account 1:

  • SIP User ID: grandstream1 (let the PBX know who you are)
  • SIP Authenticate ID: xYlkDIKDF93kCDK (used to register)
  • SIP Authenticate Password: 123456 (used to register)
  • SIP Caller ID: 6778 (used to dialing and receiving calls)

SIP account 2:

  • SIP User ID: grandstream2
  • SIP Authenticate ID: kafdpoaihYe
  • SIP Authenticate Password: 123456
  • SIP Caller ID: 6779

So when you want to call SIP account 2, you do not dial the granstream2 or kafdpoaihYe, but you dial 6779
When some internal account want to call account1, they dial 6778.

Above is for an internal call, of course, your PBX server (Fritzbox this case) should able to configure SIP Route with PSTN number to make external calls. For example, if your PBX server bind with a PSTN: +1 222-333-4444, when someone out of the company wants to use their cell phone call your work extension 6778, they just dial +1 222-333-4444, then after the IVR, dial 6778, and the PBX will route the call to account 1.

So, @chris.spiga, in most cases, the SIP User ID, SIP Authenticate ID and SIP Call ID are the same because the admin are lazy and this is easy to maintain, but they are not required to be same, and you don’t need a numeric SIP User ID or SIP Authenticate ID to register the account, but you need log in the Fritzbox to figure out how it configured and how it works. If the Fritzbox does not recognize the 620, you wont able to call it, but if someone calls to you (how does that happen? they call 620?) and you already received 2 calls, you can do attended transfer.

Another problem could be you are using the same account on 5 handsets, what’s your HS mode? if you set it as default HS1, which means the incoming call will always ONLY ring handset 1, no matter you configured it on 5 handsets. it will not ring other handsets, because you set it to do so. You need change the HS Mode to Parallel, or assign different accounts to 5 handsets, and set the account HS Mode to HS1, HS2, HS3, HS4, HS5 accordingly. Please see the pictures in my previous reply.

If you still have problems, please post your Account Settings and Line Settings to me, you can hide the blur the ID, and enable Syslog to Debug level, set Syslog server to (or any valid IP does not reachable), then capture a packets (web -> Maintenance -> Packet Capture), i just want to confirm you set everything correctly.


In the FritzBox is a little bit different.

You can create an account for an IP Phone, with the username that is minimun 8 character. Then the Fritzbox assign to the first IP Phone the short code **620, to the second **621 and etc.

When you create the account SIP on the DP750 you need to insert the username of the Fritzbox IP Phone account on the ID user SIP and also in the Authentication ID, if you don’t insert on both there is no way to Register the SIP account.

Then I add in the “Composition Plan” the code ***XXX+ so i can call the short code used by the fritzbox.

I create an account for any DP720, so anyone had his short code.

If i want to talk to someone else i digit **621 for example, same think if i want to transfer, i made a new call to **621 and then i push transfer. NO BLIND TRANSFER ARE ALLOWED.

I want another time say thanks for the awesome support, i’m proud to buy your products.


Oh nooo, another problem to solve…
The format of the XML created by the Phonebook in the Fritz box is NOT compatible with the DP750…damn


It’s better if i open another topic, sorry


I believe I find the reason why you cannot blind transfer, is because the default dial plan does not allow you to dial **621, the default dial plan is:
{ x+ | *x+ | *xx*x+ }
as you can see there are 2 stars in front of it 621, and this dial plan only allow 1 star before any numbers.
Please change your dial plan to: (notice the last | **x+)
{ x+ | *x+ | *xx*x+ | **x+}

You can find the dial plan setting at: Profiles -> Profile X -> Call Settings


I wrote in the post before. Thanks