update iOS on jailbroken iphone 3gs lose t-mobile phone service?

[Sossity]

A while ago, I bought an iphone 3GS untethered and jaibroken, so I could use it with T-mobile.

This was when at&t was the only carrier of the iphone, and t-mobile did not carry the iphone.

I got t-mobile service on it and have used it since, but when I plug into itunes, I am prompted for an update to the iOS, from 4.3. (what I have now) to 6.0.

I have always chose no update in itunes, for fear that I would lose the jailbrake, and lose my t-mobile phone service on it.

if I updated the iOS, would I lose my current T-mobile phone service with its current plan?

 

[Applejuiced]

A while ago, I bought an iphone 3GS untethered and jaibroken, so I could use it with T-mobile.

This was when at&t was the only carrier of the iphone, and t-mobile did not carry the iphone.

I got t-mobile service on it and have used it since, but when I plug into itunes, I am prompted for an update to the iOS, from 4.3. (what I have now) to 6.0.

I have always chose no update in itunes, for fear that I would lose the jailbrake, and lose my t-mobile phone service on it.

if I updated the iOS, would I lose my current T-mobile phone service with its current plan?

It depends.
Are you using ultrasnow from cydia to unlock the phone?
If you do then yes you will lose the unlock and the JB and you will be stock on a locket AT&T iphone that you cannot use.
You can always purchase an IMEI unlock for it though, they're not that expensive for a 3GS.