Maimonides explains that the prohibition of rounding prohibits the removal of sideburns, by razor, tweezers or any other means. Though it is permitted to trim the sideburns, even very close to the skin, using scissors.
Even though sideburns are enough to satisfy the Torah requirement of peyos, many Jews grow their peyos long as a way of emphasizing the commandment (Peyos sounds like pious, right?!), or simply of Jewish identification. Some will curl their peyos, while others while tuck them behind their ear. Its just a matter of individual taste, or communal custom.
Hair is also a symbol of vanity, a preoccupation of how one looks. The prohibition against cutting off the peyos reminds a person to de-emphasize his looks, and instead depend on intellect and good character. (Rabbi Samson Raphael Hirsch, 19th century Germany)
From a mystical perspective, peyos separate between the front part of the brain which is used for abstract thought that can be used for holiness, and the back part of the brain that governs the body.
With blessings from Jerusalem,
Rabbi Shraga Simmons