How do I change networks from orange uk to O2 uk

First Option:
Phone in the Other Sim and check the Phone Network Signal If Network Signal Problem not Solved So
Secend Option:
Your Phone Network IC Fault So Please change Network IC
And Network Signal Problem will Solved
if it is there isn't much you can do on this side of the network.
Contact your phone company.

There can be many ways to Unlock your phone. As far as i know unlocking by codes is the simple and safe way. I will suggest the website Unlock-Zone.com which is doing good service and they were recommended highly in the cell phone forums.
I used them to unlock my cell phone. contacted them and within 30 mins i had my unlock code and my phone was unlocked.
Hope this helps.

it may be due to network lock, you can get unlock codes here http://www.theunlockspot.com/samsung-s8000-jet/rs10wp9/
you need to specify the country and network provider

If you have unlocked your mobile it will not show O2. Contact your network provider to check it. If it is not unlocked properly you can try to unlock it again. Unlock codes are also available online like www.theunlockspot.com.

If your Iphone is officially unlocked then it should work with any (other) network compatible SIM card - just insert a friend SIM on another network (or just get a 'free' Vodafone pre-paid starter SIM for testing) and turn-on the unit - if it is locked in any way, it will tell you!
When you do a factory reset, your unit will normally reverted to original 'o2' BRANDING and defaults: this can only be removed by reflashing/reprogramming your iPhone with 'generic' Apple Iphone firmware. 'Branding' in general in an unlock hanset will not stop you from using most of the resources of your new network but 'unbranding' (andor 'unlocking') can always be performed by a qualified technician.
Hope it helps: let me know how you go! Have fun.

You need to get your Nokia phone unlocked for all networks and for that you need to contact Vodafone to get the unlock codes.

contact your network provider and ask for a sim update and a gprs install message, this will sort the problem, also you may need to change your message service cantre number, here are the following uk ones :
Network operator SMS Centre Number O2 (Was BT Cellnet / Genie mobile) +447802000332 (contract)
+447802092035 (pay as you go)
Alt: +447802000334 T-Mobile (was One2One) +447958879879 Orange +447973100973
Alt: +447973100974 Vodafone +447785016005 Tesco Mobile +447802092035 Virgin +447958879890 3 / Three +447782000800

you could try this

By doing the reset (1st temp) you will lose all your
data ie contacts, messages, photos, videos etc etc so
back them up on your pc first.
Take out your sim card and follow the instructions below :
1st temp. put this number in the keypad
*2767*3855# let it reboot(restart)
now its ready for permanent.
Put in a sim card of a network that the phone won't
except and follow the instructions below.
( If you can't type anything with a locked sim
card inserted just take it out and do the next
step without a sim card in the phone)
Don't worry if your screen shows - - - - - - - when typing
it is supposed to do this.
Permanent.
ENTER :
*7465625*638*00000000*0000000
0#
NEXT ENTER
#7465625*638*00000000#
AND THEN *#7465625# to check the locks....all locks are
inactive...these are all the locks...
network lock - inactive
subset lock - inactive
sp lock - inactive
cp lock - inactive
sim lock - inactive
activa lock - inactive
phone lock - inactive
auto network - inactive
auto subset lock - inactive
auto sp lock - inactive
auto cp lock - inactive
auto sim lock - inactive
Enjoy !
This procedure does not change your imei number at all

cantact your network provider and ask for a sim update and a gprs install message this may solve the prob.
also check the message centre number is in the phone correctly, goto message settings and message centre number, insert the correct one from below save it and then you should be able to send messages.


Network operator SMS Centre Number
O2 (Was BT Cellnet / Genie mobile) +447802000332 (contract)
+447802092035 (pay as you go)
Alt: +447802000334
T-Mobile (was One2One) +447958879879
Orange +447973100973
Alt: +447973100974
Vodafone +447785016005
Tesco Mobile +447802092035
Virgin +447958879890
3 / Three +447782000800