Does iPhone 4S need “Data Roaming” to be “Turned On” to in order to use Cellular Data?

Hi everybody!

First of all, this is my first iPhone ( iPhone 4S ).

Here is my situation,

I'm on Sprint at Puerto Rico. I have good Sprint's Signal on most places, but not at work. Since I bought the phone, it had the “Voice Roaming” & “Data Roaming” options turned ON.

Today, I decided to turn them OFF in order to monitor the Sprint's coverage all over my way back to home from work, but left the “Cellular Data” on.

In a moment, I wanted to check my Time Line at Twitter using an App.... My surprise? “Network Error | Check Your Internet Connection”

I thought it was the app, or the server.... Used another app, even Safari, but same result... But Safari popped up a message: “Data Roaming is Turned Off | Use WiFi or Enable Data Roaming...”

I turned ON the “Roaming” options and Data came back with no issues, with both Sprint and Extended (Roaming) towers.

Once again, I turned the OFF Data Roaming, but left Cellular Data On... And got same problem. I turned off and on the phone: Same result. I even make a reset of Network Settings ( in Settings>General>Reset>Reset Network Settings): Same result.

Every time “Data Roaming” is turned Off, the 3G icon disappears and Data too. Seems like the phone needs Roaming options to be always ON in order to have Data Service... But, why? If that's true, Why have “Cellular Data” option in first place?

It looks like the phone decide by itself that Data will be used only when Roam, instead of manual selection. Isn't this an option to be selected by the customer (me)? I came from Android, webOS and WinMo, and Cellular Data always worked with Data Roaming Off, why iOS doesn't? I have no much problem with Roaming at All, cuz I'd never been charged for its used, but we never know when I could! ;)

Any help will be appreciated!

(Sorry my bad English!)