My X contacted me, but we didn't talk

Dear Ladies,
I will be very thankful if you could try to explain me this behaviour:
Two weeks ago my X girlfriend broke up with me. Since then she already tried to contact me 2 times, but we never talked. I didn't answer, since first of all I was really busy, and secondly was not sure what I am going to say to her at this moment. After few hours I called her back - she didn't answer, next day I sent her short, friendly, funny SMS (just to release pressure :)). Still no reply..nothing... So my question is why is she calling me ? My guess is that she just "teasing" (or may be "testing") me if I still somewhere "near". If she has something important to say she can email, send SMS, right ? Should I answer her next time ? What if I really busy and actually can not answer her phone ? My concern is that she will think that I deliberately ignore her.