Straight talk service is provided by AT&T, Sprint, T-Mobile or Verizon, so how it is depends on which carrier you'll be using. If you choose one with no service in your area you'll get no service. (ST doesn't maintain any of their own towers,)
As far as customer service, at best there is none. Oh, you can call them, but except for the simplest things - activating a phone, etc. - they're useless at best, and usually ill-informed about their own company's rules. But if you never have to call them about important things, it's a cheap way to get good coverage. Unlimited talk and text and 2.5GB of data/month for, if you shop wisely, about $36/month, isn't bad. I've been with them for almost 2 years and my oonly complaint is that I can't afford the phone upgrade I want. (And the one I want won't fit into my pocket.)