Queries on iPhone 3GS unlock and preserving baseband

[raksrules]

I am wanting to buy an used iPhone 3GS but whatever unlocked ones are available on craigslist / ebay.com seem to have their baseband updated to 6.15, the ipad baseband which breaks the GPS functionality.
In this case, can i buy a AT&T locked iPhone, not updated to iOS 5 and unlock it myself PRESERVING the baseband so as not to break the GPS ?
If yes then before buying the locked iPhone 3GS, what all things i need to check to ensure that i can preserve the baseband and also unlock and jailbreak it.

[dannyt]

good luck finding one that still have ios 4.0 or lower with unlockable baseband. when new ios version come out, people will update through itunes, only a small percentage that update but preserve the baseband.

[raksrules]

In that case i will only be able to get an unlocked and jailbroken with 6.15 baseband right ?
Does GPS work in such iPhone 3GS with ipad baseband ?
Will there be any baseband downgrade available ?

[Iphone Prime]

Does GPS work in such iPhone 3GS with ipad baseband ? No (not to my knowing)
Will there be any baseband downgrade available ? No (6.15.00 is impossible to downgrade to my knowing)

[monkeydance]

Try Pinkpine.com I haven't buy anything from them but ..... the last time I ask them they said they have iphone baseband and ipad unlock.

[Tomt2000]

The best and easy way are to find an iPhone 4 with fw 4.3.5 then restore iOS5 with preserve baseband.
Now you can unlock it Gevey Sim
Semi tether jailbreak
keep your GPS working

[raksrules]

^^Yes i got an iPhone 4 finally with baseband 1.59.00 and iOS 5 so i can unlock it with ultrasn0w.
You may check the following thread and give more inputs there

[iPhone Noob] Need help with unlocking/jailbreaking iPhone 4 with iOS 5 and BB 1.59.00