Download X-Lite, install & execute
Right Click w/ mouse over the app, click SIP Account Settings...
Double Click on the blank top row, enter your values there
User name: 5125551212 (your number, no spaces or dashes)
Password: case sensitive
Authorization user name: 5125551212
Domain: sip.voipwelcome.com
Domain Proxy (checked), Send outbound via: Domain
No changes to the other tabs
Click OK, ensure Enabled is checked and Click Close
Enjoy
Bookmarks