I've never had any affection toward the Blackberry line of devices, but I am definitely in love with my iPhone. If you are also a "user" (remember when that used to mean something completely different, and not good?) and if you are interested in checking out applications for your iPhone in the realm of decorating and design, I can recommend a couple.
First, if you are a fan of HGTV programs you will like the app by them called HGTV's Staging and Property. It contains a number of links to video clips from their popular line-up of home improvement shows that you can watch at your convenience, and without wrestling for the remote control or sitting through commercial breaks.
Another one is called A Home Decorating Book: What Would You Do With This Room? The author has published his top 10 "commandments" for great decorating and includes photo examples of the implemented rules. It's quite in line with my approach to decorating and offers some great tips.
There are probably hundreds of great app's out there in the interior design field and all will offer something great depending on what you, specifically, are looking to get out of them and carry with you as handheld reference. If you have any app suggestions for me (because obviously, if I checked them all out myself I'd do nothing else all day) I'd love to hear from you in my comments section.