Hi all, I thought I would add this here because it took a number of hours of digging and working with people from both Apple and Samsung too resolve. I did post most of this information as a response in a thread about this issue but cleaned up the links and thought it would be helpful to have it in Messages are under the Tips section and thus am posting it here for better visibility and discovery.
After 14 days, I almost turned my new Galaxy S4 back into BestBuy tonight due to a persistent issue of being unable to disable iMessage such that I was recieving replies to texts that I sent to friends, however their replies would go to my old iPhone or iPad. My friends who had previously communicated with me over imessage had to turn off their own iPhone's iMessage in order for me to be able to receive texts from them on my new Android phone. I visited the Apple store the night before and they got me halfway to fixing the problem by following step number 1 below. Today, I went to a BestBuy location that has a Samsung "store in store" concept in East Plano, TX and the Samsung guy got online to chat with other Samsung technicians about this issue. Here is the link to a 9 page document that goes through a number of steps how to deactivate iMessage and get texts on your Android (while still maintaining iMessage on any other Apple devices that you might still have, if you so desire): http://bit.ly/iMessageproblem
If the link doesn't work for some reason, shorten the url to get to the Samsung support page at http://www.samsung.com/us/support/ or some variation of that and type the following in the search boxin the upper right hand corner in the support section "deactivate iMessage on iPhone" in the search box in the upper right hand corner of Samsung's support pages until it gets you to the support document titled "How do I turn off iMessage on my old iPhone before I switch to my new Samsung device?" Don't worry that you aren't going through those steps before setting up your Android or that it specifies Verizon or Galaxy Tab- this seems to be a generic issue when one moves from iPhone to Android, regardless of carrier or Android model! Most of us didn't know there was an issue until well after we were into setting up our new Android phone. I used these steps and they fixed the problem. I did have to enter the model number of the Android I am using (Galaxy S4, SGH i337) to get to the pages supplied to me from the chat session at the Samsung store in BestBuy.
The long and short of my fix was 1) going to my iphone Settings under "Messages" and assuming iMessage is set to "on" scroll down to where it says "Send & Receive" and click on that. It showed my phone number along with other email and Apple related addresses. Deselect the phone number now associated with my Android device as well as any email messsages from which I didn't want to send/receive iMessages (in my case I still want to receive iMessages at email addresses associated with my iPad and MacBook). After doing those steps, close out of Settings.
Then 2) go to the itunes/apple page and change your password at the following page: https://appleid.apple.com
When you change the password on your account it supposedly deauthorizes the phone number and other addresses just deselected addresses from iMessage.
There are some other steps in between that you may need to take and are listed on the support page but hopefully that will work for you as it finally did for me.