Sony has confirmed that they are going to shut down PlayStation Mobile this summer, with the mobile store set to close on July 15 (browser purchases will continue until September 10).
You'll be able to make in-app purchases until September 10, at which point you'll also no longer be able to re-download previously purchased content. So make sure you've downloaded anything you've purchased before this point if you want it for the future.
If you've bought PlayStation Mobile games in the past, you will be able to continue playing them, but there's a few steps to take if you wish to do so. Those using a PS Vita will have to take the following action via their handheld:
Go to [Settings]> [PSN]> [System Activation]> [PlayStation Mobile]> [Activate]> [OK].
Those using a PlayStation Certified device will have to open up the PSM app and launch a piece of content between April 10 and September 10; this will authenticate your device and allow you to maintain access to your software.