Next summer SC to Yellowstone?

Be aware that reservations for lodging within the park (and for those campgrounds that take reservations, which are the bigger ones in the park) opened on May 1 of this year for NEXT summer. The sooner you can plan your trip, the better. If you can't get a campsite inside the park (which is best), your best bets for just outside the park are in West Yellowstone. In addition to the "parking lot" style one mentioned previously, there are a few more, ranging from the very manicured Grizzly RV Park to a (non-reservable) NFS campground a few miles north of the town of West Yellowstone. Several other reasonably decent private CGs in town as well. It does add about 30-45 minutes to your day to reach the main loop road in the park from "West," but it's a good alternative if you can't find space in the park, or if you need hookups. (Fishing Bridge, as noted, will be under construction next year, and is cheek-to-jowl anyway.)

As for cellphone service, with Verizon it's spotty, but ok at the major "villages" (Old Faithful, Canyon, Lake), and really good in West Yellowstone. Otherwise, don't count on it.