Grandstream dp720 keeps losing connection to base

What is this and what does it do?

https://forums.grandstream.com/t/phones-randomly-ringing/9518

IP Phones do not provide voicemail, that is a function of the PBX it is connected to, either a premise IP PBX or a cloud-based (hosted) PBX. If you are using an Asterisk-based PBX system, the usual way to access the voicemail system is to dial 98 from the phone, however you will need to know the voicemail password.

Press '*' Star for more than 4 sec then it will show the password to input if you have put it or simply press OK.

From the Granstream User Manual (Page 44):
Restore Factory Default Setting
WARNING: Restoring the Factory Default Setting will delete all configuration information of the phone.
Please backup or print all the settings before you restoring factory default settings. Grandstream is not
responsible for restoring lost parameters and cannot connect your device to your VoIP service provider.
INSTRUCTIONS FOR RESTORATION:
Step 1: Press "OK" button to bring up the keypad configuration menu, select "Config", press "OK" to
enter submenu, select "Factory Reset" (Please refer to Table 5-1 of keypad flow chart)
Step 2: Enter the MAC address printed on the bottom of the sticker. Please use the following mapping:
0-9: 0-9
A: 22 (press the "2" key twice, "A" will show on the LCD)
B: 222
C: 2222
D: 33 (press the "3" key twice, "D" will show on the LCD)
E: 333
F: 3333
Example: if the MAC address is 000b8200e395, it should be key in as "0002228200333
395".
NOTE: If there are digits like "22" in the MAC, you need to type "2" then press "->" right arrow key to
move the cursor or wait for 4 seconds to continue to key in another "2".
Step 3: Press the "OK" button to move the cursor to "OK". Press "OK" button again to confirm. If the
MAC address is correct, the phone will reboot. Otherwise, it will exit to previous keypad menu interface.

https://www.grandstream.com/products/gxp_series/general/documents/gxp_usermanual_english.pdf

A copy of the user manual for your IP phone is found here: http://www.grandstream.com/user_manuals/GXV3000_User_Manual.pdf

I have browsed through and found no mention of an RJ-11 port on the back, only two RJ-45 Network ports, one for connecting to a PC in switch mode and one for ethernet mode.

If your phone is different and DOES have an RJ-11 port (as some IP phones do), I can only assume it is to connect to a landline to offer landline services as well as IP services.

Under those circumstances of course DO NOT attempt to plug in your landline RJ-11 into an RJ-45, it will not work and you risk shorting something out.

I have the same problem Did you get an answer. Verizon wants I should talk to there expertise tech for a fee. Did anyone try it?

Access Denied

Go to internet
Type your the ip phone address
type admin as password if you never changed it
That's it

if you have a password reset disk use that.otherwise
you must use the password recovery software