Im on ATT...nave a Nokia n75...have new sim card..have new and charged battery....On ATT....they say in a great reception area...My phone drops signal, goes on and off after I turn it on...is "location sensitive" and generally is intermittant in operation..seems to be in last couple of months...I bought a new one on Ebay and it has same or similar issues of not being reliable..I'm in San Diego

Did you change phones? Sim cards? I am assuming you have the same phone, and they switched out the sim card (or maybe not?) when you changed plans.

Also, all 4G phones are also 3G and 2G phones, and they simply pick the best available. So if you lose 4G coverage, it will simply switch to the wider 3g network and when you're really remote, drop to 2G. This effects data speed primarily, there isn't any qualitative difference between them for voice and text.

It sounds like you might have something screwy with your sim card when the plan changed happened, I would call T-Mobile or visit a store and ask for a new sim card and be vocal about the poor reception after the plan change. Changing plans shouldn't normally effect reception, only changing phones/networks.

I myself experienced reception issues like yours, and the problem was a bad simcard. I'm sorry for the vague answers, but I think your best bet is to go to a T-Mobile store. They should replace the sim card free of charge.

To Unlock it from Network Lock get the Unlock code from
www.theunlockspot.com

Nokia N75 Unlocking Instructions Warning : Do not enter any wrong unlock codes on your Nokia N75 mobile phones. If you enter over a certain amount of wrong unlock codes on your Nokia N75 mobile phone, your phone may get hard locked and sometimes become unusable.
1 - Switch on your Nokia N75 without any sim card.
2 - Don't bother as to what is displayed on your Nokia N75.
3 - Compose #pw+CODE+1#.
4 - The Nokia N75 would then display the message "SIM Restriction Off" and will be unlocked!

Note :For Nokia N75 mobile phones locked to the network Fido or Rogers in Canada follow these instructions :
1 - Switch on your Nokia N75 without any sim card.
2 - Don't bother as to what is displayed on your Nokia N75.
3 - Compose #pw+CODE+7#.
4 - The Nokia N75 would then display the message "SIM Restriction Off" and will be unlocked!

The letter p appears if you press the button star(*) three times quickly
The letter w appears if you press the button star(*) four times quickly
The symbol + appears if you press the button star(*) two times quickly
The CODE you need to enter is the unique unlock code for your Nokia N75

Here is a step by step guide to put it back in.

http://www.wireless.att.com/support/tutorials.do?tutorialsCategory=Getting+Started&tutorialId=756870&deviceId=11240

Quick start guide
Your Nokia E75 is a business device that adapts to your
free time, as well.
Read these first pages to get started, then use the rest
of the guide to explore what new features Nokia E75
brings to you.
SIM card, battery,
charging, memory
card
Put the pieces together, and get started with your
Nokia E75.
Insert the SIM card and
battery
1. To open the back cover of the device, with the back
facing you, unlock the back cover release button,
and lift the back cover.
2. If the battery is inserted, lift the battery in the
direction of the arrow to remove it.
/\

3. Insert the SIM card. Ensure the contact area on the
card is facing the connectors on the device and that
the bevelled corner is facing the top of the device.
4. Align the contacts of the battery with the
corresponding connectors on the battery
compartment, and insert the battery in the
direction of the arrow.

I have the exact same problem. It started abruptly a few months ago and has never stopped. I bought a new battery, but to no avail. It's definitely a hardware problem, but I've noticed it's worse in some geographic areas than others.

Test your sim card in the Nokia phone and if the cals still drop then you will need to replace your sim card. If you dont drop calls in the Nokia phone then you will need to have the device replaced. AT&T Customer service number is 800-331-0500 for replacement options.

Is the battery fully charged now???

Limited service, is when your not getting any reception, Samsungs usually always get low reception or no reception at all if the battery is low or dying... Remove the sim card, reinsert it into the handset, charge the phone and try again...

If it still doesnt work and the sim card does work in other handsets, its still covered under the Samsung warranty if its less than 12 months old.

Factory resetting the phone will do absolutely nothing with this problem

There are 3 causes of Sim Card Registration Failed, when you first turn on the phone, the sim card attempts to connect to the network if it can not do this it gives a message like Sim Card Registration failed.

1, The sim card is turned off (is it Orange) if you have had the sim card for a while and it hasnt been used they will turn it off, you need to contact them from another phone to get it turned on or get a new sim card.

2, The phone has a hardware reception problem, when it attempts to register itself with the network it can not... There is a reception problem and it requires repairs, this isnt really an easy diy job on this handset.

3, The phone is blocked, i.e reported lost or stolen. Some networks when a phone is reported will allow it to get reception but will not let it make calls, however other networks will not give it reception at all and hence you get a Sim Card Registration failed message.

I hope this helps, these are the causes of the message.

This is a "how to" on unbranding or getting rid of the Cingular/at&t junk on your phone. Should work for other carriers as well.
The benefits to Unbranding are:
-More RAM for multitasking/web functions
-ability to select network, which can save battery life
-ability to install programs not normally allowed by Cingular.
-some button changes, giving you more flexibility.

If you try this, you do it at your own risk of bricking your phone. You've been warned!

what you'll need

The Unlock code (if your phone is not unlocked)
Nokia PC Suite with NSU (Nokia Software Updater)
Nemesis Service Suite (NSS)
Your Nokia N75 (fully charged) and the PC data cable
unlocking your phone

Caution: If this process is unsuccessful five times in a row, the phone will be permanently locked to the New At&t Network. Do not attempt to enter the code more than one (1) time total. Instructions below will assist you in unlocking your device, if these steps are unsuccessful please contact us at 1-800-331-0500 or (916) 843-4685 from overseas.

This procedure can be done with or without the Att SIM inserted into the handset

# (press the # key, 1 time)
P (pause, press the * key 3 times)
W (wait, press the * key 4 times)
+ (press the * key 2 times)
Code (enter the code-10 digits Older phones or 15 digits Newer Phones)
+ (press the * key 2 times and it should convert to a + sign)
1 (press the 1 key 1 time for phones)
# (press the # key 1 time)
Your phone should say "sim restriction off" if successful.

One Step at a Time

Install Nokia PC suite, make sure your N75 is recognized via data cable
Install Nemesis Service Suite Software
If you have contacts, pictures etc on your phone, run a backup via PC suite
Make sure your phone is connected via USB, and is in a place where it will not be disturbed
Run NSS
Hit the "scan for new device" button (looks like a magnifying glass)
click the button "phone info"
click the "read" button
should have "product code" on the left
change product code to 0541358 and hit "write"
When done, restart phone, reconnect and check product code to make sure change occured.
Make sure your phone is connected via USB again, and in a secure place
Run NSU, and follow instructions
When NSU finishes, phone should restart and you should have a new Unbranded N75!


Enjoy!

with Eraser clean sim contac , If not work is the circuit is over