My opinion is CALL!! If it were me, when I did call, I'd sound as sweet as possible on the phone...happy and cheerful. Also, I'd ask to "speak to my husband", and not "is Joe available"? For me, it would almost feel like a little twinge of revenge, for her to hear how happy and cheerful I am, and asking to speak to my husband..... I mean, if the tables were turned, and I had to answer the phone when she called, and she sounded so happy when she was calling my husband, and she referred to him in some "friendly" term, it would irk the heck out of me, so why not make HER be the one that feels uncomfortable?
Now I'm not saying to call 50 times a day....just when you absolutely need to call him. Don't give it a second thought...if you should call his cell instead.
If what he is saying and doing is true...pushing her away...then she's the one that is going to feel stupid and humiliated, thinking you're the one thinking "ha, you couldn't steal him from me could you!?"