In the past, the 555 prefix was widely used for fictitious telephone numbers in film and television. No carriers assigned 555 numbers and therefore most of them were legally permissible to show on screen. Unfortunately for producers and writers, that is not the case anymore. Almost all 555 numbers are being assigned to directory assistance services and phone carriers throughout North America. Only numbers 555-0100 through 555-0199, 800-555-0199 and 888-555-0199 are still available for entertainment clearance. While I cannot assume that most people outside Hollywood really notice or care, these numbers will become quite redundant in movies. Producers and studios should get more creative.
Fortunately, there is a way you can set up and control a unique phone number for free. Google Voice allows you to create one new phone number per Google account, absolutely free of charge. You can pick the number yourself with an area code from whatever city you choose (you can pick a number to match the residence of your characters!). You are free to use this number in your film because you own it. If you already have a Voice number or do not want the number linked to your personal email, simply create a new Google account.
Google Voice also provides tools to have a little fun and promote the film, too. You can set the number to forward straight to voicemail and record your own message. It is the perfect opportunity to orchestrate a real-world tie-in to your film by having a cast member leave a voicemail message in character. Hardcore fans can call the number and leave messages that can be picked up by the producer or studio at leisure in forwarded emailed transcriptions or mp3 files. A small but classy way to help build a small community for your show!