The call first policy is great, providing you have someone to answer the phone for you, or can let it go straight to answer phone and ring them back.
Murphy's law dictates that it will be just as you and baby are drifting off to sleep, or you have just got comfy on the couch and are feeding your babe, and THEN the phone will ring!
So go with texting, or make sure you have an answerphone.
My visitors were pretty respectful, sometimes I was a bit exhausted and just played up being tired and then they would leave! hehehe
On the other hand, sometimes it was good to be able to pawn the child off to them!