We estimate the interaction between fixed and mobile usage both for voice and data services using consumer level data from April 2013 to March 2014 in a European country. We find a significant proportion of fixed voice consumption could be substituted by mobile voice, and vice versa. However, a substantial proportion of fixed data consumption, and also mobile data consumption, is generated by fixed-mobile interaction in both directions. FTTH deployment has no significant impact on fixed-mobile voice substitution. The fixed data consumption generated by mobile to fixed interaction appears to increase with FTTH deployment.