Kirsten Dunst can be seen very quickly in an uncredited cameo as a Callister employee. She happened to be visiting her partner Jesse Plemons and her cameo was unplanned.
Robert Daly's ( Jesse Plemons ) speaking style as captain, which is quite different from the way he speaks in his real life, is a clear nod to the performance of William Shatner as Captain Kirk (particularly in the way he imitates Shatner's notoriously idiosyncratic intonation patterns).
Michaela Coel's character "Shania" asks Nanette (Cristin Milioti) to make her a Brushed Suede. A Brushed Suede is what Bryce Dallas Howards character orders in the episode Nosedive (2016) (S3E1). Michaela Coel played the Airport Stewardess in that episode.