iOS 3.1.3 jailbreak questions.

1. I wanted to jailbreak my iPhone for biteSMS and iPhoneDelivery. I was wondering if those apps still support the 3.1.3 firmware.

Consult with bitesms.com My gut tells me no. I would upgrade to 4.2.1

2. If I were to only install those apps upon jailbreaking, what would be the impact on my phone's performance? All I do is text, call, and sometimes use Facebook.

If you're 3G hasn't been physically abused (I say this because my bro cracked the back of is thus water got inside and I'm convinced this slowed it down), and you are only jailbreaking for bitesms, then you should be fine. Jailbreaking in itself doesn't slow down your phone, but really it's the apps and tweaks. Stay away from winterboard at all costs if you're weary of battery and performance!

3. If I jailbroke my iPhone, and later down the road I decided I wanted to take it off, would I still be able to restore my iPhone to 3.1.3 using iTune's "restore from backup" feature or would I be forced to restore and update to 4.2.1?

The 3G is easy to downgrade using a few tools, as there are no blobs/SHSH requirements. So, it's not really as easy as restoring to 4.2.1, but you can restore to 3.1.3 is absolutely necessary.

 

You cannot downgrade and restore from a backup. If you upgrade, sync/backup, then try downgrading, the restore process will be messed up.

You CAN restore from a jail broken platform to a stock platform, however.

So yes, you can, as long as you don't start mixing iOS versions and backups.

If I were you, I would backup your phone while it's stock, then just avoid backing it up after you jailbreak it. If you don't like the jailbreak, just restore. While you CAN restore from a jailbroken platform to stock without having many issues, it's always better doing a clean restore, in my opinion.

 

Actually, I was shocked to find out the newest BiteSMS worked on 3.1.3, on my iPhone 2G.