VoWiFi with Grandstream WP826
Wi-Fi vs. DECT
Cordless phones at home are widely used and DECT established as a standard since many years. Having a good WLAN with several access points at home, you might think of using Wi-Fi instead of DECT to achieve an extended coverage.
Fritz!Box
The Fritz!Box is used in many homes and offers a high level of convenience with the integrated telephone system. Due to the built-in DECT module, this is very comfortable and the Fritz!Fons offer many functions in the interaction. IP phones can also be registered and used with the Fritz!Box. While the WLAN can be expanded very easy with additional access points, for DECT only repeaters are available. You could also use a second Fritz!Box for this purpose but since there is no roaming, i.e. the change of the DECT base during the call is impossible. Another use case can be when the Fritz!Box is connected to the DSL line in the basement and does not reach the attic. A rather rare, but with extensive IT equipment possible case is, installing the Fritz!Box in a rack that strongly shields the radio. The problem can be solved by using a Wi-Fi IP phone.
Grandstream WP810
Grandstream offers the VoWiFi phones 
WP810, WP816, WP820, WP822, WP825, WP826 and WP836.
The setup is shown here using the WP826 as an example.
Setup
First, connect the IP phone to the WLAN. On the phone, under Settings ▸ Network ▸ WLAN, select the network and password. Then in the Fritz!Box under Telephony ▸ Phone devices ▸ Set up new device ▸ Phone ▸ Select LAN/WLAN IP phone and enter assign a Username and a Password. After that, access the web interface of the IP phone by entering its IP address in the browser. The IP address is displayed by pressing the arrow up button on the control pad of the phone. Now log in as admin. You then have to enter a specific code on the phone, which is displayed in the browser. You can then assign a password. In the menu under Accounts ▸ Account 1 ▸ General settings ▸ assign an account name and enter the IP address of the Fritz!Box as SIP server. SIP user ID and Authentication ID are the user ID specified during the setup in the Fritz!Box in the last step as username and under Authentication Password enter the password defined for this purpose.
Internal Calls
Out of the box, the Grandstream does not allow dialing of phone numbers which start with **. However, this is necessary to call internal numbers of the Fritz!Box, such as other telephones or the answering machine. Therefore, you have to adjust the dial plan. To do this, open the web interface in the browser and go to Accounts ▸ Account 1 ▸ Dialplan. To be able to dial internal numbers, you have to add the existing rules by **x+
Answering machine
In order for messages on the answering machine to be signaled on the phone, under Accounts ▸ Account 1 ▸ SIP Settings ▸ Basic settings ▸ SUBSCRIBE for MWI must be activated. The access number for voice messages is stored under Accounts ▸ Account 1 ▸ General settings. It is the username@fritz.box which was defined when setting up the IP phone in the Fritz!Box.
Phone Book
Since the phone book of the Fritz!Box does not
comply with any standard, it cannot be used for the WP810. A common data source
could be the application Synology Contacts, if you have a Synology NAS to synchronize the contacts by CardDAV with the
Fritz!Box and LDAP with the WP810. All contacts from the iPhone can be exported
with the app Export Contacts Pro
in VCARD format and imported in Synology Contacts. With the App even selected
groups and contact photos are exported and shown in Synology Contacts. The file
can also be converted with the Python script 
CardDav2GrandstreamXML
to Grandstream's XML format. For this, in addition to Python VObject has
to be installed. While converting, I got an error for some entries. These could
be traced back to the labels I assigned by myself, for example.
item1.X-ABLabel:Parents. By
deleting these entries before the conversion, everything worked fine.
Pros & Cons
Configuration in browser via web interface
Background picture for screen
Speakerphone
Wi-Fi 6
USB-C PD Connector
240x320 pixels LCD
Bluetooth 5.0
Proximity Sensor
Configurable video source for door station
Configurable Buttons for door station
Not IP classified (offered by the almost identical model WP836)
CardDAV Phone Book
Contact Photos
Own Ringtones
Display on in base
Back to main page