Step 1:

Go to settings

Step 2:

Go to my device

Step 3:

Select Call

Step 4:

Scroll down to Internet Call Settings

Step 5:

Tap on Accounts and then Add account

Step 6:

Add Username (SIP username) then add the Password (you will need to get this from the TMS) then add SIP Server (The one which is applicable to your account)

Step 7:

Tick set as Primary account

Step 8:

Click optional settings, Authentication Username must be the SIP Username as well

Step 9:

Outgoing proxy must be set as Sip Server applicable to your account

Step 10:

Click the button on the left of your Home button at the bottom of the phone, and then select Save

You will need to tick receive incoming calls to register and receive calls from this account.

In addition, If you now press the back button, you can edit Use Internet Calling to "ask for every call"  This will then give you an option to dial out via Internet Call or Mobile Call. 

You can gain access to the password by following these instructions( I am not allowed to send via email or tell you on the phone)

You can gain access to the password by logging into your TMS account and clicking on the Select Account button. Then go to Extension Manager, then click on the extension that you want to install. Click  Send password button. This will open a window that has the SIP Server and SIP Username visible. The SIP password however will be starred out. To see the password, click Send Auth Key, an Auth Key will be sent to your Email address, copy and paste this Auth Key into the blank Auth Key box. Now click show password and your SIP password will be visible.