s105 - Setting CSD or GPRS using *#VSWAP#

[tangobythebay]

Using *#VSWAP# (which I learned in this forum, very cool), I set my phone to use "Voicestream GPRS" (option 1), which means I access the internet on GPRS always. However, every time I turn it off and then back on, the setting automatically switches to "GPRS Preferred" (option 3), which in my case, always seems to use CSD.

I know that I could cancel T-Zones and just use CSD. I'm curious, how can I lock the setting to "Voicestream GPRS" (option 1)?