Testing individual telephony applications is extremely difficult. The innovations being rolled into Adhearsion before this release will dramatically help the testability of telephony applications. After this release, all applications will be relatively testable to ensure QA programmatically. Some of this functionality will be built upon SIPr.
FreeSWITCH is another open-source telephony engine that's been catching on over the past couple years and offers some interesting benefits to application frameworks like Adhearsion, including some Asterisk presently cannot offer. Adhearsion's dialplan and other framework features will be available to use FreeSWITCH-powered Adhearsion applications.