On Your Web Store
Market your app on the homepage (or any content slot) on your Web store. Use your merchandising engine to present the app download banner if your users search or browse for items related to the app platform. For example, show your iPhone app banner when customers search or browse for anything related to an iPhone. If your customers are searching for iPhone related goods, chances are they own an iPhone and would use your app.
Barnes and Noble promoting their iPhone App
1-800 flowers promoting their iPhone App
Amazon.com promoting their new Android App
On Your Mobile Web Store
If you already have a mobile web store, promote your mobile app to customers who browse your mobile store using the same platform.
Amazon.com promoting iPhone App to an iPhone user on their Mobile Web site
In Your Brick and Mortar Stores
Use window and wall space to promote your mobile apps to your brick and mortar customers. Also consider promoting your app(s) on till receipts and handing our flyers about your app at the checkout. You could even have a demo station with a secured iPhone for customers to try the app.
Barnes and Noble offered a free Starbucks to every customer who downloaded their iPhone app. An embedded 3D barcode in the app could be scanned to get the free coffee. This promotion drove over 500,000 downloads of the Barnes & Noble iPhone App.
Email and Text Message Campaigns
Notify your existing customers via email that you have created a new mobile app. Make sure to include links in the email to either the app store or in Apples case to open iTunes. Also consider sending your customers a text message to notify them that you have an app. On certain platforms such as Android you can include a hyper-link to the app in the text message.
Ralph Lauren promoting their iPhone app via a dedicated email campaign
Gap include a link to their iPhone app in many of their emails
Via the App Stores
Try and get your app featured in the respective app stores (Apple App Store, Android Marketplace, Blackberry App World, etc) and make sure you provide compelling screenshots and information about your app.
Amazon got their Android App featured in the Android Marketplace at launch
Fandango got their Movie purchasing app featured in an Apple iPhone TV commercial
To sum it up, with mobile applications, it's not a "build it and they will come" situation. Make sure you put as much effort into marketing as you do with development if you want to succeed.
This post is the final of 4. To catch up on previous posts, check out: