Basically you have two options for establishing your connection, cellular modem or WiFi. Currently we have data phones with Sprint and At&T that we use for working on the CSDS VSN RTK network and our Trimble Access data transfer. They work pretty well but have noticed that the AT&T phone will drop the connection more often. The story I heard is that with all millions of smart phones out there, the providers data networks are getting overwhelmed and drop the data over voice. It is proving to be a problem in our LA office, and are probably going to switch over to a WiFi connection instead. We also have a Sprint MiFi card that allows use to connect using WiFi instead of a cellular modem. The slick thing about it is that will host up to 5 mobile devices at once, which may be your best bet to cover all of your needs. The connection works great and download speeds are pretty amazing for mobile PC use. The only down side is that the battery life is limited to about 4hrs of continuous data streaming, so buy the extra car charger.
To set it up in your DC, you need to create a connection in your Windows Mobile Settings -> connections -> add a new modem connection. You need to know the dialing string for your provider. If you are running Trimble Survey Controller, the set up is under the Configuration -> Dial Profiles. You will need to know your IP address and port. After all that, you need to assign that dial profile to your survey style under Configuration -> Survey Styles -> (select your VSN RTK style or create one) -> Rover Radio -> Dial Profile.
Best best is to contact the guys over at CSDS (California Surveying and Drafting Supply, http://csdsinc.com/) and they'll take care of all your CA VSN RTK network needs.
Hope to helps, and good luck with the VSN RTKhaos