The incident happened around 9.30pm outside an address in Dumbryden Gardens in the Wester Hailes area of Edinburgh.
Paramedics were attending to an emergency call at one of the properties when someone entered the vehicle and stole a mobile phone.
Inquiries are ongoing to trace those responsible and anyone with information is asked to come forward.
Constable Callum Donaldson from Wester Hailes Police Station said: “It is extremely disappointing that someone would look to target an emergency service vehicle that was responding to an emergency service call.
“We fully expect the local community to be equally as outraged and would urge anyone with information that can assist this investigation to contact police immediately.”
Those with information can contact Wester Hailes Police Station via 101 and quote incident number 2486 of December 25. Alternatively, an anonymous report can be made to the charity Crimestoppers on 0800 555 111.