Hey Jose - I'm sorry to hear about your friends' experience.
However what you are suggesting is very strange.
Here's what happens. As you may already know - when you send an echo to somebody who does not yet have echoecho installed - they receive an SMS inviting them to try the service.
At this point if they choose to click on the link inside the SMS they are taken to the page http://m.echoecho.me - you can try this yourself in your mobile phone browser if you like.
If they do not have a data plan or a smartphone with a web browser it is unlikely they would even be able to make it past this step.
However assuming they do have a phone with internet access (but a phone that is NOT one of the echoecho supported models - i.e. it's not a BlackBerry, iPhone, Android, Windows Mobile or Symbian phone) then there are no further steps your friends can follow.
Nothing is downloaded to their phones so it's not possible for their phones to be affected in any way.
The only thing I can recommend is that they turn their phones off and on - and whatever problems they might have are likely to disappear.