(Original post by debt!)
I have not had any experience with the Xperia U, however its had middle of the road specs, therefore you will get some great deals at a reasononable price.
For the tech specs see: http://www.gsmarena.com/sony_xperia_u-4437.php
key ones to note: dual-core, 5MP camera, 512 RAM
Not sure if this handset will be in direct competition with the iPhone, however may be worth a pop.
With regards to the apps, there are loads of free apps on Play Store (formally Android Market), which is the equivalent to the Apple Store.
Passwords, are also built into all android phones. You can have a nifty locking screen (see attachment below).
Are you already set on getting a deal through 3 Mobile, as there may be some better deals out there, see: Best Mobile Contracts - Xperia U