Wouldn't recommend it unless you do network/telecom stuff for a living, it has a bit of an ongoing time cost in maintenance... some of the SIP trunking provide

Wouldn't recommend it unless you do network/telecom stuff for a living, it has a bit of an ongoing time cost in maintenance... some of the SIP trunking providers that have more focus on the consumer market such as voip.ms do let you define your own custom IVR and menus, to accomplish pretty much what I described, without having your own SIP-speaking system registered to it persistently. You should be able to define a voip.ms IVR destination as your cellphone.