If i jailbreak an iphone can i unlock it then remove jailbreak?

So my Mum just got given an iPhone 4 by her brother, she needs to unlock it to be able to use it with her network but she doesn't want it jailbroken and doesn't won't to have to pay for it… So if I use jailbreak to unlock the device could I then remove Cydia and it would still be unlocked?

How to input videos from laptop to iphone 4s?

I know i must use itunes for it but i don't know how it works and where do the files go after you input them to iphone. If anybody could tell me exactly that i'd be so grateful.
ps: i already have downloaded itunes on my laptop.

Internet access for unlocked iPhone 4?

My friend is selling me her unlocked iPhone 4 and I was wondering if I can use it without getting charged for data usage, if I use only the Wi-Fi from my house to go onto the internet and apps like instagram… Will I get charged?

Needs help trying to start iphone 3gs?

I tried to restore my Iphone but it wouldn't turn on. Do you think it's broken or it's just something else? Because I've tried everything to make it start up but It won't.

Upload stories to FanFiction.net?

I usually do my Internet surfing through my iPhone 4S, and I've only recently stumbled on FanFiction.net.
Is it possible for me to upload stories on said website through my iPhone?
And if so, how (step-by-step, please!)?

Does it cost money to upgrade?

I have the iPhone 4s and my upgrade is due and I was wondering does it cost money to upgrade to the iPhone 5 when it comes out

My iPhone 3GS keeps losing signal?

I have a iPhone 3GS 5.1.1 bb 6.15.00 which is jb recently been having a problem that I have no signal or 3G while in the house but do when I go outside any ideas