how to access certain cck fields from a module?

I'm currently programming a module with which one can send out SMS from a drupal site. For the site I'm making this, I used the modules usernodes and node profile, so that every user profile is a node. In these nodes are various cck fields.

My question is: how can I access the cck field, where a users mobile phone number is stored, from my module and use it from there?

Also my Goal would be that in the module settings page, one could chose, which cck field is the mobile number field, so that stuff like that doesn't get hard coded.

Any help is highly appreciated.