Doesn the society tell us to not use electronic devices for field service activity?
No, I have not found any information pointing to this fact yet (let me know if I am wrong). There is repeated information about “keeping accurate records” like KM 9/88 p3 for instance. Many articles mention to record the information, in fact one article KM12/02 p8 mentions that people have used various means to note their activity “some use a calendar or diary. Others carry a blank field service report slip with them”. The gist I get from most of the articles is: record your information accurately so that you can give a truthful report and keep up with your return visits so that you can be a better minister.