There is virtually no cell phone access in the wilderness areas of Botswana. People who absolutely cannot go without normally hire a satellite phone and bring it with them. Many people go to the bush precisely because there is no access — part of the point is getting away from the pressure of being accessible 24-7. I’m sure you’ll keep this in mind, but just in case: if you do bring a satellite phone, PLEASE do not use it anywhere other than in your own tent and in consideration of others.