Using it on my Mitel 5330 IP phone. Worked for a long time then started cutting out. Replaced batteries in Vista M22 amplifier even bought a new headset still have same problem

You must contact your Mitel phone system administrator. This is a complex question that could have many answers. This is not a 5330 phone question.
Good Luck

First, you have to unplug the Ethernet cable from the phone to turn it off. Second, remove the receiver from the hook. Third, hold the #6 on the keypad as you plug in/turn the phone back on until you get a prompt on the screen. Follow the prompts using * and # to signify yes or no respectively and you should come across an option to perform a factory reset. I hope this helps.

It sounds as though there's something wrong with the microphone.

Have you tried using an external headset?

Pick groups are programmed??

Problem with network or maybe cable. Phone can not connect to Mitel phone system.

The Voicemail isn't in the phone itself, but usually in the phone system. You will need to contact your system administrator or telephone vendor to have the mailbox reset. While they're at it, have them update the username.

It sounds like you've got another DHCP server running and that the phone is not getting the proper settings from the network.

It sounds like you have a short in the wiring. Mitel has their own cordless headset for the 5330 model phone... it is awesome in every way. Battery life, range, clarity, etc

You cannot change the time from the phone. Your system administrator must change the time in your PBX. If you have the latest version, you can have your PBX sync with an internet time server and will never have to update again!

I just had the same problem with my Mitel 5330 IP Phone. The solution? Press #20 then the extension number: example, my phone with extenaion 555 has the problem, go to that phone and type #20555 on the keypad.