Taxi - Telephone (Book 9‪)‬

It's Ulrike's birthday. Carmen tries her luck at buying practical presents rather than pretty ones. Ulrike's brother and mother are delighted, however, for Ulrike those presents come with challenges that Carmen had not bargained for.
Far more than expensive presents, Ulrike would appreciate it if Carmen had more time for her, alas Carmen seems to spend more time with her pupils than with her, and Ulrike begins to wonder if this relationship is really worth all the effort.

Taxi - Telephone is the 9th book in the Taxi series.