STUNT BANANA provides a Caller ID spoofing mechanism much like SpoofCard and other available services, but at a much reduced cost, if you don't mind doing the setup yourself and having a much more minimal UI. STUNT BANANA also allows you to host new phone numbers (DIDs) for your devices and use a SIP Phone app, such as Zoiper to place and receive calls, as well as get voicemail for those lines sent your email as MP3 files.

Spoofing Caller ID is not illegal. Impersonating other people and committing fraud is. If you bulk call people with spoofed caller IDs, your SIP trunk provider will notice and you will get taken down and possibly receive criminal charges. Don't be dumb.

The scripts clone, compile, and install Asterisk for you, so if you want to use this with an existing Asterisk install it's going to take some hacking.