Accessorising your device with an iPhone case which looks like a hand gun could cost the user up to $4000 and time behind bars, police warn.
Overseas, the accessory was slammed by the New York Police Department who called it "ridiculous" and warned people not to buy it.
After hearing it could be purchased online and shipped to New Zealand for under $100, police here have added to the criticism.
Jason Ross, a manager at NZ Police, said "on the face of it" the phone case would be regarded as an imitation gun and police would treat it as such until proven otherwise.
"We would strongly advise against carrying such items given their considerable potential for causing unnecessary alarm to the public, whether this is intended or not," Mr Ross said.
"Police are regularly called regarding people carrying what appears to be a firearm, which later turns out to be a toy or imitation.
"Such calls will always prompt a full and immediate response from police, include the deployment of armed staff," he said.
Anyone found carrying the item could face a $4000 fine, imprisonment, or both, police warned.
The NYPD 112 Precinct posted a picture of the offending cases on Twitter with the message: "I would NOT suggest purchasing this cell phone case, which was designed to look like a firearm. #BeSmart #BeSafe."
The accompanying image, taken by the Queens North NYPD School Safety Division, shows what looks like a handgun tucked into the back pocket of a woman's shorts, but is actually a mobile phone.
Gun crime has been in the headlines in America, following the massacre of nine people at a church in Charleston last month, which reignited the debate over gun laws.