Clear Nav, LX Nav, Butterfly, Vega varios...

Is there an open protocol that allows these varios to talk to any and all Soaring_Software/PDA that implements interoperability with them?

Or does your choice of vario also commit you to a brand of Soaring_Software/PDA?

I realize that you don't necessarily need your Vario to inter-operate with you PDA, but isn't that half the point of spending $2-3000 on a new vario?