I’m looking to incorporate some in-class feedback from students, test exam questions, etc. by allowing students to answer questions by sending text messages.  I don’t intend to do it very often, and thus don’t want to pay anything–everybody wants something for free, right?  But, I was interested to see if anybody has used this and prefers of the of several services that offer the service.  It seems that there are several options (in the US): like smspoll.net or polleverywhere.com.  Thoughts or recommendations?