having just brought a Android we put a mobile Broadband pack on it. I had always understood this worked in broadband zones and would be locked out unless you texted unlock to 233. This seemed to born out by a reference to text unlock on 233.
when we did our first trip out of zone a text came in saying that you were moving out of broadband zone and would be charged 50c a MB I had not texted unlock 233.
On rechecking the website I find references to both having to text unlock 233 to use national Data and moving to a straight charging system.
When I rang 202 they gave me an answer which i didn't fully understand that Data on Android couldn't be fully locked.