Software - Mobile Phones

There are huge limitations, as a matter of fact. For starters, you don't have the Standard Library at your disposal (only recently was this problem sor of solved with the advent of uSTL by Mike Sharov: http://www.dev-archive.com/wireless/Article/33076/0 )
At the moment, uSTL is supported only on GCC-based IDEs.

*You rarely have a proper file system on most mobile devices
*There's no real multitasking, let alone multi-user support (iPhone however is a pioneer in this respect as it supports proper multitasking
*There's no virtual memory so you have to be very careful about resource usage and memory leaks and finally, there's a very limited stack size (typically 8 kilobytes!) which means that almost everything that's allocated on the stack in mainstream programming has to be allocated on the heap.
Other than that you have limited peripheral device support (you can't connect your mobile to a printer, for example). This isn't all, but I think it gives you enough pointers.

I said "limited peripheral support" which isn't quite the same as "completely unsuupored". You can use bluetooth connection too, in some devices not all them support that, and in some models, you can't connect anything. You simply have to dowload the stuff you want. But the real issues are the ones listed above: memory, multitasking, STL etc.