Firms charging an identical price will always be the case in perfect competition since any firm that charges more than the going market price will sell nothing. In price-setting among oligopolists there is usually a bit of dispersion among the prices.
So if there is some dispersion of prices and service among a few oligopolists, how much is this price dispersion and what are the differences in service? Take a look at the companies providing domestic airline services in Canada and use this to describe the differences.