If you're looking at the HTTP header that is sent to your HTTP server from Phone.com's UP.Link gateway, you will notice a difference in the User Agent field. The UP.Link gateway very cunningly adds the name and version number of the gateway. Good work Phone.com! This is the sort of stuff we like! If only other gateway developers could do the same..
  
If your user is passing through a Nokia or Ericsson gateway, the User Agent will look something like this:

But, if he's passing through the UP.Link gateway, the same user will look like this:

Which clearly identifies the gateway UP. Link and the version number 4.1.0.1. Great stuff for when you want to add extra functionality for those users who are coming in via that type of gateway. Several of the other popular gateways are now also identifying themselves via the HTTP_VIA header.