I am relooking at how I do things, but I use a service from direct page, that used to be my beeper company.
They give me a local telephone number as potential for a voicemail, but I leave a message stating DO NOT leave a message, this is for emergencies only. It can receive text messages and about 1/2 the patients leave them. It sends a text message with the telephone number (and perhaps message) (ala beeper) to my cellphone and my NP's as well.
I forget what it costs, but about $15.00 a month as I recall.
