I have been giving some serious thought here, reading all responses.
So, let me get this correct, you are somehow experiencing BIS for up to 3 months at no cost from whomever the carrier is, and I can understand why you wouldn't post it here.
Would an OS upgrade affect the current situation you are currently enjoying?
There may be in fact a risk of losing your free BIS service if you upgrade your BlackBerry device, regardless if it's an upgrade via (DM) Desktop Manager, or a complete wipe, using any third party software, such as BBH-Tool, or BBSAK.
Why would you take a chance to upgrade the OS, knowing that you're receiving BIS at no cost, do you really want to take a chance and find out when the free ride is over?
Personally, even though it shouldn't matter if upgrading the OS for your BlackBerry device, which begs another question.
What BlackBerry device are you currently using by the way?
It's difficult to post correct information here when you haven't posted what device you're using, and what official OS7.0.0.xxx/7.1.0.xxx I can offer you as of current.
Ultimately, it's up to you how you what direction you wish to take, but as Joe mentioned above, it's at your own risk.
We can only suggest, and guide you here the best we can, sometimes with very little info from our members and guests.
Thank you, and good luck.