I have an iPhone myself and I've actually found that the in-built apps like the calendar, maps, notes and clock all work really well in terms of organising myself.
Th calendar is great because you can create multiple calendars for different things (i.e. Family Occasions, work, deadlines etc) and you can set it to give you reminders very easily.
The maps also works well because it's not only easy to use but by saving your home address into it it can direct you home from anywhere with the tap of a button, it's very simple!
However, the inbuilt app I find the most helpful is the 'Clocks'. It has four different functions; a timer, a stopwatch, times from around the world (you can add cities of you choice) and alarms. The alarms I use everyday because every alarm you create gets saved so you can easily use it again, and you can very simply set it to go off on certain days (such as weekdays).
If you're still considering getting an iPhone I really would recommend it because they are so simple to use, everything works very easily and all in all they are very dyspraxic-friendly!
I hope this helps,