A devCert from symbiansigned.com is not needed at all during development for the user grantable permissions:

LocalServices NetworkServices ReadUserData UserEnvironment WriteUserData

...and coming in 3rd FP2... the Location permission will be added to the user grantable list.

With self-signed you can sign a sis file to run on any phone. In this case the installer displays warnings, lists the requested permissions for the user to grant.

I have to confess I did not understand this after reading the materials and I suspect that many others are suffering from the same confusion. I thought that a devCert for each IMEI was needed for self-signing.

I think a lot of traffic coming to symbiansigned.com and many postings here could be eliminated if self-signed is promoted more prominently. The self-signed option is not even mentioned in "The Complete Guide to Symbian Signed" (2nd ed 11/07). Rather the guide encourages "developers" to pursue publisher IDs. It fails to mention the requests from individual developers are not valid.

Run makekeys one time on your PC to create a self-signing certificate.

Code:
makekeys -cert -password yourpassword -len 1024 -dname "CN=Test User  OU=Development OR=Company  CO=FI EM=test@company.com" mykey.key mycert.cer

signsis <application_name>.sis <application_name>.sisx <Path>\mycert.cer <Path>\mykey.key
With Carbide C++ you can set the cert and key in a "Build Configration" in Project Properties instead of using signsis at the command line.

Note: I found I had to uninstall devCert signed app before I could install the self-signed version. Otherwise the installer reported "File Corrupted".