Like the above posted mentioned, Scopetel is a good place to start.

Emerson does employ telecom. majors too as they provide DCS integration services, with platform telecommunications network included as part of their scope.

Bartec Vodec specialises in PA/GA systems, so they're worth looking at as well.

I suppose subsurface service companies including Schlumberger, Halliburton, Baker Hughes and Weatherford do employ quite a number of people coming from electronics engineering backgrounds and I doubt majoring in telecom. will harm your chances with them. Give it a go with them.