Satelitte dish tv/internet/phone
For phone, cellular is the best option. You want a company which offers nationwide coverage without extra fees. Verizon is what I have, and it works pretty well. There are a few places in the country where you have to pay outrageous roaming charges, but I'd say I've had 'free' coverage about 95% of the places I've been.
I prefer 'tri-mode' service, since analog seems to be available in places that digital can't reach, but then I understand that analog cellular is being discontinued in 2008, so that may not be necessary any more.
A good batwing antenna with booster can provide adequate TV reception in many areas. The other TV option is satellite. Your service options are Dish or Direct TV (or possibly a receiver which receives 'free' programming). Your dish options are a manual one on the ground or a dish on the roof (or both). Most of the roof dishes are for when you are stationary, but there are some which claim they work in motion (probably not of much value in a trailer

.
Internet is a bit less clearcut. You can do by dialing up over your cell phone, or use a specified internet service from many of the cell companies. Or use WiFi, dial up or campground facilities (only if you don't need it regularly or for long periods), or use satellite.
Satellite can be expensive, although if you use a manual, ground mounted dish it can be not too unreasonable. At least one of the services allow you to hook a TV LNB to the dish, so you can get both with one dish (still have to deal with 2 companies though).
If you do have internet, you may be able to use one of those internet phone services