Use this method to hard reset your Samsung SGH-i637 Jack phone: Enter *2767*3855#. Warning! All your data including contacts, messages etc. will be lost! Copy all your necessary data/Contacts/Messages etc. to SIM or make backup to your PC before full reset! Take out SIM card before full reset.
1. Once the handset has rebooted to the Today Screen, enter the following code: *2767*3855#. The handset should display a message “Formatting, Please Wait…”
2. The phone will reboot after the Full Reset as this is normal operation.
OR How to Reset My At&T SGH-I637 with buttons?
Samsung i637 Jack hard reset with buttons / keys

To reset the handset's factory settings, via buttons, follow the steps below:
WARNING: This Reset will Delete ALL added Data from the Handsets Memory
1. When the handset is powered off, Press and Hold the 5 key
then power on
the handset
2. Press either the 1 key (Master Clear) or 2 key (Master Reset) at the Format Menu screen then press the Y key (Yes) at the confirmation prompt
Note: To turn the SGH-I637 (Jack) on or off simply Press & Hold the power button
, located on the upper left side of the handset.
Samsung i637 Jack hard reset with Firmware update
SGH-i637 Upgrade Tool download from manufacturer's website.
You will need Samsung i637 Jack USB Data Cable (Included In Retail Box - P/N: APCBS10BBE)
Samsung i637 Jack hard reset from menu
1. From the home screen, press the left soft key for Start
2. Press the left soft key for More
3. Press the left soft key for More again
4. Select Settings
5. Select More (7) to display more settings
6. Select Security (1)
7. Select More (7) to display more settings
8. Select either Master Clear (2) or Master Reset (3)
9. With Device highlighted, press the left soft key for Yes to confirm resetting the handset to the factory default settings