Crowley is shown using a cell phone throughout the series.
Initially, Crowley used the Goblet of Blood or required summoning in order to communicate with other people. Sometimes, he chose to just teleport in order to meet with someone, especially for the first time.
For those he is close acquaintances with, Crowley keeps their contacts on his cell phone. He is mostly seen talking with the Winchesters or his demon minions.
Crowley keeps a list of contacts of allies. Otherwise, he uses a Goblet of Blood.