Iphone 4 iOS 5.1.1 sends iMessages to Android which doesn t receive obviously

Alright. A quick story line about my situation, I've been reading a lot of similar problems but not quite the same. So maybe somebody can clue me in on a possible fix, easiest as possible. I would GREATLY appreciate that.

I've had the Samsung Galaxy S (Rogers) since the day it came out. Months later, I hated the reception it was giving, so I had to get a new phone from a different carrier, so I chose Bell (since I've many an issue from Telus in my younger teenage days). And so I naturally kept my samsung as a spare emergency phone and tucked it away to never be used again, dropped the bill to 20 a month and that was that.

So now I live in a different town 2 hours away from where I used to live, and my iPhone has been a great phone as far as everything goes. My girlfriend has been needing a new phone as her old flip phone is about to bite the dust. To save us both a lot of money and time, it was easier just to add unlimited texting to the rogers samsung and change the number to a local, as opposed to adding a new phone to my plan.

That was done in a matter of minutes, no hassle. Checked the samsung about a half hour after the changing the number, and all was changed just fine.

Tested it to see if it would send texts. Perfect. My iPhone 4 received it nearly instantiously. BUT, when I send the samsung a text, it sends it as an iMessage? ***, why? It makes no sense in any way, nor should it EVER make sense. But, it is what it is. Here's the kicker. My iPhone 4 has NO problem sending a call to the Android. So that's at least a little bit of good news. It's just the iMessage having issues, because the Android doesn't have it lol.

This isn't just MY iPhone 4, her brother also has one (same fully updated iOS), and we asked him to send my Android a text, but his also does the same thing. He gets the texts, but sends them as an iMessage. So this is a problem, and a huge issue to not just ME, but a LOT of people it seems.

Any ideas? And sorry for the long story, just seemed easier to explain myself so everyone has a clear understanding of the situation.