Should I call back???

[Cameron Berens]

Sent out my first 200 yellow letters and have already received 11 call backs through the Google Voice number associated with them. I'm pretty happy with the call back percentage even though it only seems 1 so far has the potential to turn into a deal. The first couple calls were the hardest but now the conversations are flowing pretty naturally and I am enjoying speaking to each person. Even though I have gotten 11 calls not all have left voice messages but I obviously have all their numbers from caller ID. 

Being they didn't leave a message should I count them off as probably not motivated or should I still give them a call back regardless?