Hi,
This simple application turns the speakers on or off by sliding the keyboard out or closing it respectively while the call is active - making and answering the call (not while receiving/ringing).
It is just in early development phase and hence not yet uploaded to extras-devel but will soon. However, for those who want to give it a try and leave some feedback, I have attached the .deb file. I've used it, installed/uninstalled, restarted device, without any problem hence you shouldn't have any either. If any, just uninstall and let me know.

TO DO:
* Use proximity as well [DONE]
* Create a control panel applet for settings (options to also open dashboard while speakers are active if any other files are open and of course to choose between proximity or keyboard action) [DONE]

TO INSTALL:
*open x-terminal
*sudo gainroot (assuming you have rootsh installed from repo)
*dpkg -i psswitcher_0.1-1_armel.deb (assuming you are in the same directory as this .deb file)

OR

Open the file from File Manager to install. (EASY)

TO UNINSTALL:
*sudo gainroot (assumption as above)
*dpkg -r psswitcher

OR

Simply uninstall from Application Manager.

UPDATES:

0.2-3 is in Extras-testing now.

NOTE: Answering and ending calls using camera button is yet not supported in Skype and GTalk calls.

*Version 0.2-3 (Current)
*Changelogsince 0.1-9)
- Issues with bluetooth headset is resolved
- Options to enable camera button to toggle proximity while proximity is in use
- Disabling proximity by half-pressing camera button while making or answering a call will last for that whole conversation. It can't be later enabled within the same conversation.
- Other minor fixes

*Version 0.1-9
*Changelog:
- Information banner to show proximity state everytime its toggled
- Delay timer upto 10 seconds
- Other minor fixes

Again usage instructions file /usr/share/doc/psswitcher/README.Debian.

This package is just uploaded to extras-devel and as soon as its there I'll promote it to testing. Thanks

update: package is now in extras-testing


*Version 0.1-8
*Changelog:
- Supports Bluetooth headsets now
- Pressing camkey while answering/calling deactivates proximity
- Pressing camkey for around half a second toggles proximity
- Ability to use keyboard and proximity concurrently
- While opening keyboard proximity is temporarily disabled
- Option to set delay when turning speakers on via proximity
- Usage instructions file /usr/share/doc/psswitcher/README.Debian
IMPORTANT: Due to dependency problem for now it can only be installed giving sudo dpkg -i --force-depends psswitcher_0.1-8_armel.deb

*Version 0.1-7
*Changelog:
- cam key presses more accurate (meaning- long press ends phone call and quick short press toggles speakers and presses falling in between isn't effective)

*Version 0.1-5
*Changelog:
- Proximity Fixed
- Option to select distance before turning the speakers on has been removed coz it was for different purpose actually
- Minor fixes in control panel plugin UI
*Bug-tracker has also been added but as of now its not active yet. When it gets, I'll be pushing it to testing.

*Version 0.1-4
*Changelog:
- GUI interface in control panel for configuration
- Option to automatically open dashboard added
- Option to easily end call added
*Now available to download from extras-devel(BEWARE OF THE RISK OF ENABLING EXTRAS-DEVEL IN APPLICATION MANAGER)
*However, you can use the attached .deb file instead until I push it to extras-testing for testing purposes.

-----------------------------------------------------------------------------------------------
PLEASE NOTE THE FOLLOWING BEFORE INSTALLING:
[config file is in /home/user/.psswitcher/config]
[using proximity and other shortcuts at the same time will interfere and may cause random issues so please avoid doing so]
[just changing from true to false or vice versa will either disable/enable the shortcut]
[for "Distance", higher the value, further you can hold before the speaker gets activated ]
[please do killall PSSwitcher for changes to take effect] -- EDITED
[In config "Use Switcher", "Double Tap", "Open Dashboard" have no effect. I'm planning to implement them with control panel plugin for disabling the application, double tapping to end call and opening the dashboard while turning the speakers on respectively]

*Version 0.1-3
*Changelog:
- Proximity sensor shortcut is added
- Config file to switch shortcuts
- Phone UI's button is updated when toggeling speakers
- Some minor fixes

*Version 0.1-2
*Changelog:
- Sometimes only works when redoing is fixed.
- Camera focus button shortcut is added.
- Ineffective when headphone is plugged is added.

PS: Big thanks to qwerty12 or else I would have been still banging my head .