Two TV ads for the Motorola DEFY smartphone featured the handset being used in various different scenarios, including being splashed at a pool party and dropped on a dancefloor.
A text slogan said: "Water resistant, scratch resistant, dust proof - it's life proof."
However, three complainants accused the ads of having "misleadingly exaggerated the durability of the mobile phone", because they had accidentally dropped their Motorola DEFY handsets and the screens had cracked.
Motorola "strongly" refuted the claims and said that the DEFY featured a display with "specific resistance to bumps, impacts, scrapes and scratches". The firm said that the chemically strengthened screen "acted as an 'armour' to reduce the introduction of flaws by end users".
Motorola said that the ad featured the same phone being "dropped in a number of takes", and was shot live without enhancement or computer generated imagery. The firm said that it had conducted extensive product testing on the DEFY, and claimed that returns in the UK were "very low".
However, the Advertising Standards Authority (ASA) ruled that viewers were likely to interpret the ad as claiming the phone was "entirely damage-resistant" and "would generally withstand damage in the scenarios depicted and from day-to-day".
The watchdog was particularly concerned about the scene in which the phone was dropped from a height by someone in a nightclub.
"The scene that involved the phone being dropped onto a dance floor and the on-screen text 'dance floor proof' and 'it's life proof', suggested the phone would also not be damaged when it was dropped from the height shown in the ads," said the ASA.
"We noted the evidence Motorola submitted and acknowledged the testing was conducted in circumstances designed to be more extreme than were likely to be encountered by consumers, so as to detect failures.
"We also noted, however, we had not seen any evidence that directly reflected the dropping scenario depicted in the ads and that, in the evidence submitted, each of the tests resulted in damage to the phones, including their screens cracking.
"Because we had not seen evidence that dropping the DEFY from the height shown in the ads would not damage the phone, we concluded that the ads misleadingly exaggerated the performance of the product.
The ASA told Motorola that the ad must not be broadcast again in its current form and warned the firm to "ensure future ads did not misleadingly exaggerate the performance of products".
This is not the first time that Motorola has been criticised by the ASA. In August the firm was banned from claiming its Atrix handset was the "world's most powerful smartphone", as it actually had less processing power than a rival device.
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