After five minutes or so you were able to get a signal and the minute you started talking, your call dropped again. A couple of minutes later your phone rings and in the middle of the ringtone - it dies again.
You curse sun spots, your cell phone carrier and even your phone - it may not have been any of those things. It may have been a someone using a personal cell phone blocker. For under $50, people can purchase a device that effectively kills all cell phone reception in a 2-to-40 foot area. The devices themselves are roughly the size of cell phones, usually black and have three rubber capped antennae on the top about one to two inches in length. They can be hidden easily in a pocket and don't have to be removed from clothing to work. Someone would just need to reach into their pocket, push the button and all cell phone signals will be halted.
These devices are illegal in many countries, but that doesn't stop them from being sold online and shipped. Customs can't catch everything so some people are getting them and using them. It's currently a problem in Europe with only a limited number of incidents in the United States.
However next time you're trying to talk to someone and you keep getting dropped, look around to see if anyone is looking at you and smirking, it may just be someone with a cell phone killer.