"Within 3 months more than 80k people used Spy Your Love mobile
application to spy their partner’s mobile phone (7000 couples are still
daily using application).
Spy your Love is mobile application that comes
with controversial solution of partner's cheating and trust issues.
Solution is based on mutual and voluntary monitoring/sharing of phone
calls, SMS and Facebook messages. Mutual means that both partners are
spying each other. Partners are losing 15% of their privacy but getting
90% assurance that their partner is faithful." (more)
Grain-of-Salt Alert: This excerpted from a Slovakian press release, hence the odd syntax. It is, however, an interesting spyware app concept.