A security firm is warning iPhone users not to use the Safari browser to dial telephone numbers because of a bug that could allow attackers to stick victims with a phone bill full of pricey 900-number calls. The bug likely isn’t unique to Apple’s iPhone, but the most popular device of the moment is the one that SPI Labs chose to check out.

“It’s possible a similar type of issue applies to Treos or Windows Mobile devices,” the company wrote on its blog post. Respondents to the post suggested that built-in browsers in other phones, such as BlackBerrys or those from Nokia, are also susceptible given that they provide the same functionality of calling a number from a Web page.