I am not sure if my relationships are normal, but one of my best friends is someone I dated years ago. We went so far as to have *gasp* sexual relations before deciding that it wasn't there. That was actually the deciding factor. We had everything except the physical intimacy.
My boyfriend knows about the prior relationship. He has no problems if I have long conversations with my friend. It doesn't bother him that I tell my friend, "I love you." A few factors have made this a comfortable situation.
1.) I was completely honest about the relationship from the start. I made very sure that my bf was comfortable with the situation.
2.) I tell my boyfriend when I talk to my friend.
3.) I don’t make my conversations private when my boyfriend is around. I don’t take my calls to another room, and my bf can hear the entire conversation if he so desired.
Now, in this situation, if I was to start hiding the conversations, or if I was dropping everything to talk to, or be with, my friend, then I am sure my bf would have a problem. And rightly so. I think in the case of your story, any deviations from the norm would start to increase suspicion. How long it would take would depend upon whether or not she was ok with it from the start. Of course, any hint of increased intimacy in the husband's voice shoots her suspicion right up there.
On the other hand, if the wife knew nothing about a continued friendship between her husband and his ex, then it would only take one phone call.
ETA: I just thought of something. A lot of the situation would depend upon how close the husband was with his ex. If the husband and his ex were really close in their relationship, the current wife's suspicions would come on a lot faster. Even if she was previously ok with the friendship.