In advance of February's software development kit, Apple has updated the iPhone's features.

Features added include

- Maps with location
- Webclips
- customized home screens
- SMS multiple people at once
- videos now support chapters
- subtitles
- languages
- music now supports lyrics

Apple CEO Steve Jobs unveiled the latest iPhone features during his Macworld Expo keynote.

The Maps interface has been streamlined in the latest update, adding button in the bottom left that finds your location on a map. Apple worked with Google and Skyhook Wireless to use both Wi-Fi hotspots amd mobile masts to create the location feature.

"The iPhone is not standing still," Jobs said.

Users can also create Web Clips - icons on the home screen that take you directly to user-specified websites, including to the exact spot you have zoomed into. iPhone users can also customise their home screen by repositioning any of the icons, and even create up to nine different home screens to flick between.

According to Jobs, Apple has sold 4 million iPhones to date, averaging sales of 20,000 phones per day. That gives the iPhone a 19.5-percent market share of the U.S. smartphone market, second only to BlackBerry maker RIM, which has a 39 percent market share.

What's more, Jobs said, the iPhone's market share is equal to the combined percentage of the next three largest companies - Palm, Motorola, and Nokia.

The device has also been made compatible with iTunes Movie Rentals (available internationally this year, according to Apple), film fans can rent films on their computer or Apple TV, transfer them to their iPhone, and watch them on its screen. On-screen film navigation has also been improved, you can move forward or backward through movies by chapters, select alternate language tracks and view subtitles, if available.

The update is available now.