Samsung SIM card issues!

get a sim card that you have payed for service with then register the phone with them

Hi,
Contact your service provider and get the unlock code for your Samsung SGH-A707 from them or else you can get it from online sites. Try Prounlocking.com ,they provide codes at affordable price.
Unlocking Instructions:
1 - Switch ON your Samsung SGH-A707 with a NOT ACCEPTED SIM Card.
2 - Compose : #7465625*638*CODE# (or *#7465625*638*CODE#).

NOT ACCEPTED:Use a sim card from a network other than the network your Samsung SGH-A707 is locked to.
CODE: Its the unique Unlock Code for your Samsung SGH-A707 that you get either from your service provider or from online sites.

Computer card Unlocking is very Big process,So that You can use the Unlock code....also in computer card Unlocking you need to use Cable,Software,USB port,Boxes etc,so take big time ,it's risk process,cost High also,So that i would suggest the Unlock code the simple method to Unlock Your Samsung SGH-A707 SYNC phone,You need to Unfreeze means specify the Network ,Country it locked now?
You can get the Unfreeze Code at
Simpleunlocking and Unfreeze the Phone from Lock...


Samsung SGH-A707 SYNC Unlocking InstructionsWarning : Do not enter any wrong unlock codes on your Samsung SGH-A707 SYNC mobile phones. If you enter over a certain amount of wrong unlock codes on your Samsung SGH-A707 SYNC mobile phone, your phone may get hard locked and sometimes become unusable.
1 - Switch ON your Samsung SGH-A707 SYNC with a NOT ACCEPTED SIM Card.
2 - Compose : #7465625*638*CODE# (or *#7465625*638*CODE#).

NOT ACCEPTED: We mean, to use a sim card from a network other than the network your Samsung SGH-A707 SYNC is locked to.
CODE: Its the unique Unlock Code for your Samsung SGH-A707 SYNC.
Each Samsung SGH-A707 SYNC mobile phone has an unique unlock code. You can buy the unique unlock code for your Samsung SGH-A707 SYNC mobile phone using the form above.

It may be due to network lock,
you can check it with other sim card ,if it remains the same problem ,it may be locked to particular network wont accept any sim card other than the particular network ,you can unlock it and used to other network,try here
http://www.prounlocking.com/samsung-sgh-a707-sync/rs8wp9/

you can check it with other sim card ,if it remains the same problem ,it may be locked to particular network wont accept any sim card other than the particular network ,you can unlock it and used to other network,try here http://www.prounlocking.com/samsung-a707/rs8wp9/

phone not working with my Go Phone sim card. I receive message "sim not allowed MM#3" after I turn on device.

I had the same exact issue.  Also, I couldn't send, receive or view old messages.
What I had to do was power it up without the SIM card.  You should get a message that there is no SIM card - that's ok.  Then power it down, re-install the SIM card and power back up.  My problem went away.

*2767*3855# - FULL E2P RESET after you do this the phone will reset completely. DO NOT LEAVE YOUR SIM IN IT WHILE DOING THIS OR YOU WILL LOSE YOUR NUMBERS.

At this stage, call AT&T is probably the best bet. Call back until you get a more knowledgable technical support rep.