You shouldn't have any problem with a signal in Townsend. I have T-Mobile and always have a decent signal within the city limits of Townsend.
Coverage in the park is another issue. There are no towers within the park and thus no coverage that I have been able to find. Some folks have discussed obtaining satellite phones for use in th park if a person must be able to communicate by phone, but it can be quite expensive.
Personaly I think it's kind of nice to be able to escape and be or remian out of touch in the park for a few hours