How to put multiple conditions on a field, using Views 3?
Consider module Views Contextual Filters OR (which only has a dev version today). Excerpt from its project page:


  ... provides a views plugin which modify query to support OR conditions for contextual filters.


A few issues on Drupal.org that may be of some help:


Using OR in filters breaks contextual filters.
Views AND/OR Contextual filters two ways.


There is also this comment in the support forum.