Can two way speakerphone be disabled on a 1140E?

Ensure that the speakerphone feature is not disabled. Some phones have a dedicated button or an option in the phone menu to enable or disable the speakerphone. Look for this option and make sure it is turned on.
Or Reset the phone to factory settings. Refer to the user manual of your 25423RE1-A phone for instructions on how to perform a factory reset. Keep in mind that this will reset all settings and may delete any personalized configurations.

Try a different phone on the same router, does that fix it?

Hello, depending on the status of the call the buttons will change automatically. Be aware that you may not be the initiator of the call so you may not have all the features. I hope this helps. If not you may contact me at: http://www.liveperson.com/nortel-guy

should work, no problem.

That is not possible

If you are running C6E or later firmware, then the following keypad sequence is used to reset all provisioning paramaters to a "factory default":
[*][*][7][3][6][3][9][MAC][#][#]
Where MAC corresponds to the MAC address of the IP Phone which can be found on a label on the back of the IP Phone.
Since a MAC address can contain the letters A-F, then letters A/B/C can be entered via the [2] key on the dialpad, and letters D/E/F can be entered via the [3] key.
For example, an IP Phone with MAC address 00:19:E1:E2:17:12 would be reset to "factory default" when the sequence **73639001931321712## is entered on the keypad.

You need to use an AC power supply on the base IP Phone 1140E for the backlight on the Expansion Module to work.

1. Reset the phone by disconnecting and re-connecting power.
2. When the Nortel logo appears, press each of the four soft keys in sequence.
3. If no other configuration changes are required, press OK repeatedly until the “PC
Port? 1-ON 0-0FF” option appears.
4. Press 1 to enable the PC Port or 0 to disable the PC Port.
5. Select OK to confirm the change.
6. Restart the IP Phone.
When the IP Phone is restarted, the firmware sets the PC Port status accordingly

C1B is ancient UNIStim firmware. You cannot downgrade to it. Try converting to a more recent UNIStim version. You can download firmware from www.nortel.com/support.

Is it the only IP phone? Howstable is the network?