Where can I find a user manual for the Avaya 5621SW IP desk phone?

Here is a link to follow. Go to page 20. http://www.telephonemagic.com/PDFs/Avaya-IP-Office-manuals/Avaya-partner-ETR-phone-user-guide.pdf

Your phone needs to be added to the same hunt group as hers on the phone system.

Quick Reference Guide (PDF):
http://support.avaya.com/css/P8/documents/003877145

Full User Manual (PDF):
http://support.avaya.com/css/P8/documents/003877145

Not directly. You can get a Plantronics "Voyager" blue-tooth base unit. That can go into the headset port.

Is this an IP Office or Definity?

SAy what? I have no idea what you are asking. You are correct, teh 46xx phones are 1/2 duplex, nothing you can do about it.

Does the phone boot up? Have you tried a different phone at your desk?

Try to login manually from the avaya not from the computer. it will log you in. but you might also need to check with your CCO (call center operation desk) and which software you are using to log in and check if you have an outside access, if its still not working submit a trouble ticket at your company's website. reinstalltion the application will not work if the access is not there. avaya are very safe phones and i am also using the avaya 4620sw ip phone. it happens sometimes when you login using the softphone but try to login using the hard phone. it should log you in, but will it solve the purpose. you need to check. All the best.

download the user guide here

http://support.avaya.com/elmodocs2/4610/233784_4.pdf

Have your system admin movethe extensions ports. You have a definity or S87xx series.....that is the only way.