If you want to make a 9P interface to SMS without running Hellaphone, you should start by looking into the RIL daemon. If I remember correctly, it runs at the L

If you want to make a 9P interface to SMS without running Hellaphone, you should start by looking into the RIL daemon. If I remember correctly, it runs at the Linux level (not Java) and drops a socket somewhere. The Java libraries for making phone calls, texts, etc. work by sending commands to that socket. You can read/write that socket yourself and use it to e.g. send SMS