The most common reason for getting the message "can't connect to server" is because there is no connection to the internet. In order to verify this, try to open your browser and see if you do have internet connection. If you are not able to use your browser you are either in an area without coverage or you are not configured correctly in your phone. To see your phone configuration do the following:
Go to Home -> Settings -> Connections -> Wireless Manager
See if your Phone Conection is On or your Wi-Fi connection is available (you will have to set up your Wi-Fi in order to be connected).
If you are able to use your browser, go to Vlingo icon and click it. This usually resets its functioning if there were any problems. If it is still not working, power off and on your phone, check your internet connections and try again.