Melodica

The melodica was another instrument used by Joy Division during a select few recording sessions: briefly on "Decades" and quite predominantly on "In a Lonely Place", which only exists as a rehearsal recording (this recording can be heard in the "Heart and Soul" box set). New Order used the melodica a number of times and were said to have "inherited" it from Curtis, who purchased one after hearing it used by dub-reggae artist Augustus Pablo. Sumner apparently didn't look after the original very well and was seen to smash it to bits over the back of his head during a New Order gig at the 'Tabernacle' in London shortly after the release of their first album 'Movement'

Source : http://en.wikipedia.org/wiki/Joy_Division

Although Sumner probably was the member most keen on changing the band's sound and constantly "move on" in new directions, it was actually Curtis who took the unusual step to bring a melodica to the studio. This, by some considered as "just a child's instrument" had found an unexpected renaissance in Jamaica, frequently used by artists like Augustus Pablo. Sadly, the only track with said instrument that Joy Division got to put down to vinyl was "Decades" where it features briefly. It was to be used more properly on In A Lonely Place which was written and demoed only weeks before Curtis' death. According to themselves, New Order "inherited the melodica from Ian" and not only used it on In A Lonely Place, they would use it on many songs recorded from then on: Truth, Hurt, Your Silent Face, Love Vigilantes, Angel Dust, Fine Time and Run Wild, and of course their Keith Hudson cover Turn The Heater On (which they recorded for a John Peel radio session as a tribute to Curtis - who had been a huge fan of reggae legend Hudson) all feature Curtis' melodica.

Source : http://members.aol.com/lwtua/eqpt.htm