The phone number shown on Constantine's business card (404) 248-7182) is a working number. When dialed it connects to an outgoing voice message from Constantine. 404 is also the area code for Atlanta, where the series is filmed and set.
Lucy Griffiths appeared as Liv Aberdine, who was supposed to be the female lead of the show. She was subsequently dropped after executive producers David S. Goyer and Daniel Cerone decided to take the series in a different creative direction. Some of Griffiths' final scenes from the pilot were re-shot, explaining why she doesn't join Constantine in his adventures as it was originally intended.
An online petition has begun, to convince other networks to pick up the show for a second season. The petition, aimed at networks such as USA, The CW Network, and El Rey, has reached upwards of 50,000 signatures.
The series does exist in the same universe as DC's shows Arrow (2012), The Flash (2014), Legends of Tomorrow (2016).
Though cancelled after one season, Constantine makes an appearance in the 4th season of Arrow (2012) and the 3rd and 4th and 5th and 6th seasons of DC's Legends of Tomorrow (2021).