I have decided to post this here as it involves Slingshot and 2talk, but not sure who's fault it is and 2talk support don't seem very interested.
Here's the problem
I have a customer with an Elastix server and anybody that rings from a Slingshot better network phone line (not Chorus wholesale line) 
cannot navigate the Elastix IVR, the only way they get through is with the timeout function.
When I look at the Asterisk log it looks like the DTMF's do not get to the server, hence why it times out.
All other lines work ok Chorus lines, mobiles are all fine.
I myself have recently changed from a Chorus wholesale(Slingshot) to a Slingshot better network line and now I cannot navigate the IVR either.
I hope someone  from Slingshot or anyone else can shed some light on this issue and has anyone else come across this?