I can't send pictures on my iPhone 4?

Okay, so I switched to a different Apple ID, and now I can't send pictures! I'd like to know why this is happening, and how I can fix it. My cellular data is on, my MMS is on. And I can't switch back to the old account, because then I'll receive messages that my sister sends from her iPod. Please help!

Added (1). My internet works fine, and I can receive pictures too.

Whts up with the textin problem for iphone 4?

My mom won't receive a text messege from me. Other people DO get my text meseges. But her phone receives text messeges from other people but why not me? I'm not bloked or anything
Btw i'm using an iphone 4

I just got an iPhone and I've already used a ton of data?

I'm on a 2gb data plan and I only got 2 because I have Wi-Fi at home. Even though I have the Wi-Fi, even when my phone is idle, it is still using up my data. I don't know what is going on with it but is there any way to get this under control or some kind of app to help out with this?

Added (1). Thank you Sora! That sounds like the best thing I could do. Now this is my first smart phone so I still have so much to learn about this.

Rage of Bahamut on iPhone and iPad?

So I'm playing RoB on my iPhone and soon I will get an iPad. When I install RoB on the iPad will it automatically use my settings from the iPhone where I'm Demons or will I be able to start with a Man or God on the iPad?

How to Export Edited Photos from iPhone?

I edited some photos on the basic Photos app of my iPhone 4 (cropping, custom rotation, image enhancement etc) and I tried to export them by opening my iPhone directory in My Computer and cut-and-paste the photos to a desktop folder. However, none of the edits are saved!

How do I export it with the edits intact without using a separate app?

FYI: I synced the photos from my desktop to my iPhone, edited them and saved them into my camera roll and then tried to cut and paste them back into the computer (I've my reasons for doing it this way, just wanted to let you know where the photos came from if that matters)