TomTom may be stepping up its efforts to produce turn-by-turn iPhone GPS through a low-key recruitment effort. A job listing for an iPhone app developer doesn't mention the company but asks for someone to develop navigation software in Amsterdam, the location of TomTom's headquarters. The term would start in May or June and last for at least six months.

While the possibility exists that it's another, smaller company developing the GPS app, TomTom was one of the earliest to express an interest in iPhone GPS, confirming its attempts a month ahead of the App Store's launch. Worries over competition and the inherent limits of the iPhone 2.x SDK, which doesn't support vector-based (directional) positioning and other resources needed to fully handle turn-by-turn GPS. iPhone OS 3.0 explicitly supports turn-by-turn directions.

Other major companies will potentially be involved, though Garmin is very unlikely to support the iPhone due to its alliance with ASUS on the nüvifone series of smartphones, which bring Garmin's familiar GPS software to Linux- and Windows Mobile-based hardware. [via GPS Review]