so typically when we have any user-facing text, we like to add in translations. The convention in hq is to import translation stuff as follows:
`from django.utils.translation import ugettext as _, ugettext_noop`

so in this case I'd wrap the text in validation error like so `_("%s is an invalid phone number")`
- use `_()` inside the instance
- use `ugettext_noop` outside the instance