diff --git a/cfp/models.py b/cfp/models.py
index d233574..0c14ec8 100644
--- a/cfp/models.py
+++ b/cfp/models.py
@@ -1,5 +1,6 @@
 from django.contrib.auth.models import User
 from django.contrib.sites.models import Site
+from django.conf import settings
 from django.urls import reverse
 from django.core.validators import MaxValueValidator, MinValueValidator
 from django.core.exceptions import ValidationError
@@ -14,6 +15,7 @@ from django.utils.html import escape, format_html
 from autoslug import AutoSlugField
 from colorful.fields import RGBColorField
 from functools import partial
+import phonenumbers
 
 import uuid
 from datetime import timedelta
@@ -483,12 +485,22 @@ class Activity(models.Model):
         return self.name
 
 
+def validate_phone_number(phone_number: str):
+    try:
+        number = phonenumbers.parse(phone_number, region=settings.DEFAULT_PHONE_REGION)
+    except phonenumbers.phonenumberutil.NumberParseException as err:
+        raise ValidationError(str(err))
+    else:
+        if not phonenumbers.is_valid_number(number):
+            raise ValidationError(_("Invalid phone number"))
+
+
 class Volunteer(PonyConfModel):
     site = models.ForeignKey(Site, on_delete=models.CASCADE)
     name = models.CharField(max_length=128, verbose_name=_('Your Name'))
     email = models.EmailField(verbose_name=_('Email'))
     token = models.UUIDField(default=uuid.uuid4, editable=False, unique=True)
-    phone_number = models.CharField(max_length=64, blank=True, default='', verbose_name=_('Phone number'))
+    phone_number = models.CharField(max_length=64, blank=True, default='', verbose_name=_('Phone number'), validators=[validate_phone_number])
     sms_prefered = models.BooleanField(default=False, verbose_name=_('SMS prefered'))
     language = models.CharField(max_length=10, blank=True)
     notes = models.TextField(default='', blank=True, verbose_name=_('Notes'),
diff --git a/ponyconf/local_settings.py.example b/ponyconf/local_settings.py.example
index 7450c91..14e5ac5 100644
--- a/ponyconf/local_settings.py.example
+++ b/ponyconf/local_settings.py.example
@@ -2,6 +2,8 @@ from ponyconf.settings import *
 
 SECRET_KEY = 'CHANGE ME'
 
+DEFAULT_PHONE_REGION = "FR"
+
 DEBUG = False
 
 LOGGING = {
diff --git a/ponyconf/settings.py b/ponyconf/settings.py
index c41d590..84dd1bd 100644
--- a/ponyconf/settings.py
+++ b/ponyconf/settings.py
@@ -128,7 +128,7 @@ LANGUAGES = [
 ]
 
 LANGUAGE_CODE = 'en-us'
-
+DEFAULT_PHONE_REGION = "US"
 LOCALE_PATHS = [
     os.path.join(BASE_DIR, 'locale'),
 ]
@@ -171,4 +171,3 @@ SERVER_EMAIL = 'ponyconf@example.com'
 EMAIL_BACKEND = 'django.core.mail.backends.smtp.EmailBackend'
 EMAIL_HOST = 'localhost'
 EMAIL_PORT = 25
-
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 5b667c3..06ef82e 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,47 +1,99 @@
 #
-# This file is autogenerated by pip-compile
-# To update, run:
+# This file is autogenerated by pip-compile with Python 3.9
+# by the following command:
 #
 #    pip-compile requirements-dev.in
 #
-asgiref==3.2.10           # via django
-backcall==0.2.0           # via ipython
-bleach==3.1.5             # via -r requirements.in
-chardet==3.0.4            # via -r requirements.in
-decorator==4.4.2          # via ipython, traitlets
-django-appconf==1.0.4     # via django-select2
-django-autoslug==1.9.8    # via -r requirements.in
-django-bootstrap3==14.1.0  # via -r requirements.in
-django-colorful==1.3      # via -r requirements.in
-django-crispy-forms==1.9.2  # via -r requirements.in
-django-debug-toolbar==2.2  # via -r requirements-dev.in
-django-extensions==3.0.4  # via -r requirements-dev.in
-django-select2==7.4.2     # via -r requirements.in
-django==3.1               # via -r requirements.in, django-appconf, django-bootstrap3, django-colorful, django-debug-toolbar, django-select2
-icalendar==4.0.6          # via -r requirements.in
-importlib-metadata==1.7.0  # via django-bootstrap3, markdown
-ipython-genutils==0.2.0   # via traitlets
-ipython==7.16.1           # via -r requirements-dev.in
-jedi==0.17.2              # via ipython
-jinja2==2.11.2            # via -r requirements.in
-markdown==3.2.2           # via -r requirements.in
-markupsafe==1.1.1         # via jinja2
-packaging==20.4           # via bleach
-parso==0.7.1              # via jedi
-pexpect==4.8.0            # via ipython
-pickleshare==0.7.5        # via ipython
-prompt-toolkit==3.0.5     # via ipython
-ptyprocess==0.6.0         # via pexpect
-pygments==2.6.1           # via ipython
-pyparsing==2.4.7          # via packaging
-python-dateutil==2.8.1    # via icalendar
-pytz==2020.1              # via django, icalendar
-six==1.15.0               # via bleach, packaging, python-dateutil, traitlets
-sqlparse==0.3.1           # via django, django-debug-toolbar
-traitlets==4.3.3          # via ipython
-wcwidth==0.2.5            # via prompt-toolkit
-webencodings==0.5.1       # via bleach
-zipp==3.1.0               # via importlib-metadata
+asgiref==3.2.10
+    # via django
+backcall==0.2.0
+    # via ipython
+bleach==3.1.5
+    # via -r requirements.in
+chardet==3.0.4
+    # via -r requirements.in
+decorator==4.4.2
+    # via
+    #   ipython
+    #   traitlets
+django==3.1
+    # via
+    #   -r requirements.in
+    #   django-appconf
+    #   django-bootstrap3
+    #   django-colorful
+    #   django-debug-toolbar
+    #   django-select2
+django-appconf==1.0.4
+    # via django-select2
+django-autoslug==1.9.8
+    # via -r requirements.in
+django-bootstrap3==14.1.0
+    # via -r requirements.in
+django-colorful==1.3
+    # via -r requirements.in
+django-crispy-forms==1.9.2
+    # via -r requirements.in
+django-debug-toolbar==2.2
+    # via -r requirements-dev.in
+django-extensions==3.0.4
+    # via -r requirements-dev.in
+django-select2==7.4.2
+    # via -r requirements.in
+icalendar==4.0.6
+    # via -r requirements.in
+ipython==7.16.1
+    # via -r requirements-dev.in
+ipython-genutils==0.2.0
+    # via traitlets
+jedi==0.17.2
+    # via ipython
+jinja2==2.11.2
+    # via -r requirements.in
+markdown==3.2.2
+    # via -r requirements.in
+markupsafe==1.1.1
+    # via jinja2
+packaging==20.4
+    # via bleach
+parso==0.7.1
+    # via jedi
+pexpect==4.8.0
+    # via ipython
+phonenumbers==8.13.4
+    # via -r requirements.in
+pickleshare==0.7.5
+    # via ipython
+prompt-toolkit==3.0.5
+    # via ipython
+ptyprocess==0.6.0
+    # via pexpect
+pygments==2.6.1
+    # via ipython
+pyparsing==2.4.7
+    # via packaging
+python-dateutil==2.8.1
+    # via icalendar
+pytz==2020.1
+    # via
+    #   django
+    #   icalendar
+six==1.15.0
+    # via
+    #   bleach
+    #   packaging
+    #   python-dateutil
+    #   traitlets
+sqlparse==0.3.1
+    # via
+    #   django
+    #   django-debug-toolbar
+traitlets==4.3.3
+    # via ipython
+wcwidth==0.2.5
+    # via prompt-toolkit
+webencodings==0.5.1
+    # via bleach
 
 # The following packages are considered to be unsafe in a requirements file:
 # setuptools
diff --git a/requirements.in b/requirements.in
index 1e44517..2b49bd0 100644
--- a/requirements.in
+++ b/requirements.in
@@ -11,3 +11,4 @@ bleach
 chardet
 icalendar
 jinja2
+phonenumbers
diff --git a/requirements.txt b/requirements.txt
index c78917b..18cc1e9 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,29 +1,60 @@
 #
-# This file is autogenerated by pip-compile
-# To update, run:
+# This file is autogenerated by pip-compile with Python 3.9
+# by the following command:
 #
 #    pip-compile
 #
-asgiref==3.2.10           # via django
-bleach==3.1.5             # via -r requirements.in
-chardet==3.0.4            # via -r requirements.in
-django-appconf==1.0.4     # via django-select2
-django-autoslug==1.9.8    # via -r requirements.in
-django-bootstrap3==14.1.0  # via -r requirements.in
-django-colorful==1.3      # via -r requirements.in
-django-crispy-forms==1.9.2  # via -r requirements.in
-django-select2==7.4.2     # via -r requirements.in
-django==3.1               # via -r requirements.in, django-appconf, django-bootstrap3, django-colorful, django-select2
-icalendar==4.0.6          # via -r requirements.in
-importlib-metadata==1.7.0  # via django-bootstrap3, markdown
-jinja2==2.11.2            # via -r requirements.in
-markdown==3.2.2           # via -r requirements.in
-markupsafe==1.1.1         # via jinja2
-packaging==20.4           # via bleach
-pyparsing==2.4.7          # via packaging
-python-dateutil==2.8.1    # via icalendar
-pytz==2020.1              # via django, icalendar
-six==1.15.0               # via bleach, packaging, python-dateutil
-sqlparse==0.3.1           # via django
-webencodings==0.5.1       # via bleach
-zipp==3.1.0               # via importlib-metadata
+asgiref==3.2.10
+    # via django
+bleach==3.1.5
+    # via -r requirements.in
+chardet==3.0.4
+    # via -r requirements.in
+django==3.1
+    # via
+    #   -r requirements.in
+    #   django-appconf
+    #   django-bootstrap3
+    #   django-colorful
+    #   django-select2
+django-appconf==1.0.4
+    # via django-select2
+django-autoslug==1.9.8
+    # via -r requirements.in
+django-bootstrap3==14.1.0
+    # via -r requirements.in
+django-colorful==1.3
+    # via -r requirements.in
+django-crispy-forms==1.9.2
+    # via -r requirements.in
+django-select2==7.4.2
+    # via -r requirements.in
+icalendar==4.0.6
+    # via -r requirements.in
+jinja2==2.11.2
+    # via -r requirements.in
+markdown==3.2.2
+    # via -r requirements.in
+markupsafe==1.1.1
+    # via jinja2
+packaging==20.4
+    # via bleach
+phonenumbers==8.13.4
+    # via -r requirements.in
+pyparsing==2.4.7
+    # via packaging
+python-dateutil==2.8.1
+    # via icalendar
+pytz==2020.1
+    # via
+    #   django
+    #   icalendar
+six==1.15.0
+    # via
+    #   bleach
+    #   packaging
+    #   python-dateutil
+sqlparse==0.3.1
+    # via django
+webencodings==0.5.1
+    # via bleach