[Q] Unlock Phone? - Sony Ericsson Xperia Mini, Mini Pro, Xperia Pro, A

Hi there,
I've recently got a new phone - Xperia Active.
It's locked to a Skinny Mobile Network as the packaging says "This phone will only work with Skinny Sim!". - I bought this from site similar to ebay. The phone is brand new - won in a competition.
http://skinny.co.nz/
I spoke to customer service who told me that it would cost $30 to unlock it but if i am with them for 9 months, it's free.
The questions I had in mind are:
1) Is it safe to flash a custom firmware on a 'locked sim network' phone?
2) What is the steps I have to take to flash a custom firmware i.e. expeacer's muiu or Real ICS ??
3) After 9 months i decide to unlock my phone (sim lock), would anything stuff up i.e if i stick another sim card in, the menu doesn't show up for entering the network unlock code.
Update:
checked my bootloader settings. It says: Unlock bootloader allowed: No

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Furbus said:
The questions I had in mind are:
1) Is it safe to flash a custom firmware on a 'locked sim network' phone?
2) What is the steps I have to take to flash a custom firmware i.e. expeacer's muiu or Real ICS ??
3) After 9 months i decide to unlock my phone (sim lock), would anything stuff up i.e if i stick another sim card in, the menu doesn't show up for entering the network unlock code.
Update:
checked my bootloader settings. It says: Unlock bootloader allowed: No
Click to expand...
Click to collapse
Custom firmware means a combination of custom Rom and custom kernel
1. You can only flash custom Rom's which have support for locked bootloader and I don't think you will get any problem with it (I'll better leave it for someone else to answer because I've never used a network locked phone)
2. As said above you can only flash custom Roms with locked bootloader and you can NEVER FLASH A CUSTOM KERNEL. You cannot use Roms which require their own custom kernel.
3. NO. you can stick up any sim after unlocking your phone with the unlock code your network provider (skinny) gives you . As your network provider said you can purchase the unlock code by paying 30 bucks or wait for nine months and get it from them for free. Either way you need a unlock code to use other sim cards.
and I'm sorry you can never use Roms which require custom kernels even if you have unlocked your network locked phone because your phone says "bootloader unlock allowed:NO" it means you can never use custom Roms like Cyanogenmod or other custom Roms which requires their own kernel to be flashed prior flashing the Rom .
To flash a custom kernel you need a unlocked bootloader and to unlock your bootloader your phone has to say "bootloader unlock allowed:yes" unfortunately yours says NO
EDIT: I learned that you could ask the network provider to change the bootloader status to yes after getting through the prescribed period of 9 months or after paying 30 bucks. After getting it to show 'yes' you can unlock the bootloader and flash custom kernels.
HIT THANKS IF I HAVE HELPED YOU!
sent from my smultron