You don't need - or want - a short code from Twilio: those are very expensive (often many thousands of dollars). Instead you only need a long code, which is equivalent to a phone number. These cost about $1USD/month to get from Twilio.
To get started, you must first set up your own account on Twilio. Sign up at http://www.twilio.com. Within Twilio's system, you will:
Create your own account.
Provide a payment mechanism (usually a credit card).
Purchase at least one incoming phone number from them. You should get one in the same area code as your regular phone numbers, but this number cannot be the same as your regular phone number and must be acquired from Twilio.
From the main Twilio dashboard, click on the "#" sign to see your active numbers.
Click on + to buy a new number.
Search for and select an appropriate number to purchase.
Configure that phone number, within Twilio's website, to look like this. Note especially an SMS URL which is required by Twilio.
Assuming that you're using VSys Live and/or VSys Anywhere, enter URLs similar to the above. This tells Twilio to post incoming messages and message status changes directly to VSys using a special interface in VSys Live.
If you have only VSys Live, enter its URL - with the /download/twilio path included - as the location for A MESSAGE COMES IN, and leave PRIMARY HANDLER FAILS blank.
If you have both VSys Live and VSys Anywhere, put the VSys Live URL - with the /download/twilio path included - for A MESSAGE COMES IN and then the VSys Anywhere site under PRIMARY HANDLER FAILS.
If you're not using any form of VSys Live, ask us and we can give you a placeholder URL to put here.
Twilio sends your actual incoming messages to this location. Don't randomly put something in here: if you've got questions, ask us!