Make iPhone use GPS-only location services
The iPhone's systems are optimized for battery life. From the chip design to the OS, battery conservation takes precedence over all.

GPS chips are massive power consumers. Read these answers for more information on GPS chip power use. Due to this, the iPhone will always prefer to find its location with wifi/cell tower triangulation, then refine with GPS.  The phone will often quickly cycle the GPS chip on and off, confirming location as needed. (remember, computers think in microseconds or smaller)

Since the iPhone is not a dedictaed GPS, you likely will never find a way to force it to become one. You might try an iPhone GPS application, many of which seem to 'force' the GPS chip (and drain the battery).

For more, learn about Assisted GPS, which explains how GPS works on your phone, including iPhone. This may also explain why your carrier might be a challenge, as it might not be providing you with Mobile Station Assisted data.