The answer to this depends greatly on the type of society that you are talking about. The impact of mobile phones on developed, rich societies is much different than their impact on developing societies.
In developed countries, mobile phones are mainly for convenience and entertainment. In rich countries, people use their mobiles for playing games and taking pictures and exchanging texts with their friends. (Of course, there are many uses for business--people can make business calls while driving, etc.) There are good effects (easier communication with family members, more things to do for fun) and bad (people are never out of touch with their offices and bosses), but the phones may be seen by some as just a convenience.
In developing countries, mobile phones can be much more important. In countries without good infrastructures, mobiles can be the only real way of communication. In many countries, mobiles are starting to be used the way credit cards are in rich nations; this means there are ways to buy things using your mobile. There, the functions of mobile phones are much more vital than the uses of mobiles in rich countries. In developing countries, then, the effect of mobiles is to greatly improve people's basic abilities to communicate and to buy things. These are things that have long been taken for granted in the rich world.