Microsoft has released Word flow for iPhone app which means they will be able to enjoy goodies windows phone users have been enjoying from quite sometime. But it has some few extra features that windows phones lack, for instance, it has theme support so you can skin your keyboard with graphics and your own pictures.
By default, it uses white theme but you can go for black theme too which looks great on black iPhone. It is US only for now so you will have to switch to US store to download it. Here is a video of word flow in action on iPhone.
If you like typing with one hand, you will love it. Download link