What do I do after I defeat the Wall of Flesh in the Mobile edition of Terraria?

In the mobile version there is no hard mode... Have I 'beaten' the game?

With the release of the 1.2 patch to mobile versions in December 2014, there is now a huge amount of content post-Wall of Flesh to be experienced (to be honest, the quantity of post-Wall of Flesh content is probably greater than the pre), as well as some new pre-Wall of Flesh content as well. The mobile release as of December 2014 is roughly equivalent to the PC's 1.2.1.2 patch, but as more patches are released you should be able to find a summary of the changes here. Hardmode and the 1.2 patch add an extraordinary amount of content to Terraria so a comprehensive list of changes would be far too long for this format, so instead I'll do a brief run-down of some of the more important changes. For more information, your best bet is to surf through the Wiki.

NOTE: You will need to create a new world in order to experience much of the new content.

Half-blocks

Hammers have a new purpose: making half-blocks. These allow you to create slopes instead of blocky stairs, and also allow you to create Waterfalls. While visually it's not always that noticeable, they have been included into the terrain generation algorithms and will result in a "smoother" world that's easier to travel across. They also have huge potential for new building designs.

Making the World bloody...

The second major difference you might run into is The Crimson, which is a new biome that has a 50% chance of being created at world generation, and replaces the Corruption. This brings with it a host of new crafting materials, items, monsters and a new pre-Hardmode boss: The Brain of Cthulhu.

Of Pyramids and Giant Trees

The next few differences you might encounter are changes to existing biomes. Deserts now have a chance to contain a Pyramid structure, which will contain a treasure room containing some brand new loot. You might very well also notice Giant Trees scattered around the landscape. Some are just big trees, while others are hollow inside and generally have a chest containing some more brand new loot.

A Bee in your bonnet

The Jungle has also undergone a few changes. When exploring the Underground Jungle you may now run into a Bee Hive microbiome which will allow you to summon and defeat another new boss; the Queen Bee.

Ice, Ice Baby

You may have had some worlds previously that contained a Snow Biome. These have been drastically changed and now each world is guaranteed to generate a large one, with a larger Underground Snow Biome beneath it.

The ancient spirits of light and dark have been released

Defeating the Wall of Flesh will activate Hardmode, beefing up the difficulty of pretty much every biome in the game and giving you access to all of the Hardmode-only content. Of which there is lots.

Lihzahrd is hard to spell

Delve deep enough into the Underground Jungle and you'll find the Lihzahrd Temple - although you won't be able to enter it until you have defeated one of the new Hardmode bosses: Plantera. In the PC version, all three 'original' Hardmode mechanical bosses, The Destroyer, The Twins and Skeletron Prime must be defeated before Plantera can be summoned. This is not the case on the mobile and console versions. On the console and mobile versions, only one mechanical boss must be defeated before Plantera can be summoned. Once inside the Lihzahrd Temple, you will be able to find an altar that allows you to summon another new boss, the Golem. The Hardmode Jungle is also the only place you will find naturally occurring deposits of Chlorophyte Ore.

Friendly Automated Characters

There are also a bunch of new NPCs for you to acquire for your village. With the exceptions of the Stylist and the Angler, which are (currently) exclusive to the PC version, you should be able to find all of the NPCs listed there in-game.

This is Halloween

Craft yourself a Pumpkin Moon Medallion and you'll be able to start the Pumpkin Moon event (but be warned: it's hard). Your world doesn't need to be in Hardmode to use it, but two of the crafting materials are only found in Hardmode.

Have you been Naughty or Nice?

Craft yourself a Naughty Present and be prepared to have hordes of Christmas-themed enemies try their hardest to end you when you kick off the Frost Moon event. This event is even harder than the Pumpkin Moon and is the current end-game content for the Mobile Edition. Don't expect this to remain the case however.

Mobile Exclusive Content

As a mobile player you will have exclusive access to certain content, such as Oktoberfest and Thanksgiving seasonal events with the latter having a boss: Turkor the Ungrateful.

Essentially, yes, you have. There are a few other things that it's possible you haven't done yet, such as find all of the possible town NPCs, but unless you plan on sandboxing, there's no real reason to seek them out, either.

If you choose to be optimistic about the possibility of a future Hardmode update to the mobile version, you could farm the Wall of Flesh to prepare yourself with the best gear possible, but as it is, you've more or less "won."