It would be cool, but a project on itself. Definitely doable though.
Seems your service can be used anonymously... a bit expensive though. But, criminals may be your customer to make extortion calls as well as elites may use it to book call girls.
As I can see, you are talking about making it open source. Hows that going to financially benefit you ? Will it be partially open source, so that use of your service remains mandatory ? Or you plan to monetize it from BitKit API ?
Its not completely anonymous, but yes it can definitely be exploited in some manner.
In regards to abuse, we have very clear terms of use, so does the telco provider. The call receiver can also block his number, no questions asked.
But how would someone who does not know of the service know that he is being called using this site or service ? To him it will just be another number that he is getting a call from.