In the 0.7.4 release, Minecraft: PE introduced external server listing.
Open Minecraft: PE, and on the Main Screen, tap Play.
Tap the Edit button, on the top right corner.
A new button will appear. Tap External. It is next to the Edit button.
A new window will appear to add the server details. You will have to type all the details, theServer Name (can be anything), the Address (external IP or domain of the server), and the Port (defaults to 19132).
After you have done this, tap the “Add Server” button on the right.
The server will be shown on the top of the Play list. To join the server, tap the slot.
Tutorial courtesy of Shoghi Cervantes