diff --git a/app/models.py b/app/models.py
index 6037bd26d..74b0af79a 100644
--- a/app/models.py
+++ b/app/models.py
@@ -224,7 +224,7 @@ class Service(db.Model, Versioned):
     _reply_to_email_address = db.Column("reply_to_email_address", db.Text, index=False, unique=False, nullable=True)
     _letter_contact_block = db.Column('letter_contact_block', db.Text, index=False, unique=False, nullable=True)
     sms_sender = db.Column(db.String(11), nullable=False, default=lambda: current_app.config['FROM_NUMBER'])
-    prefix_sms = db.Column(db.Boolean, nullable=True)
+    prefix_sms = db.Column(db.Boolean, nullable=True, default=True)
     organisation_id = db.Column(UUID(as_uuid=True), db.ForeignKey('organisation.id'), index=True, nullable=True)
     free_sms_fragment_limit = db.Column(db.BigInteger, index=False, unique=False, nullable=True)
     organisation = db.relationship('Organisation')
diff --git a/tests/app/dao/test_services_dao.py b/tests/app/dao/test_services_dao.py
index 76c06d088..c45ce0272 100644
--- a/tests/app/dao/test_services_dao.py
+++ b/tests/app/dao/test_services_dao.py
@@ -93,6 +93,7 @@ def test_create_service(sample_user):
     assert service_db.branding == BRANDING_GOVUK
     assert service_db.dvla_organisation_id == DVLA_ORG_HM_GOVERNMENT
     assert service_db.research_mode is False
+    assert service_db.prefix_sms is True
     assert service.active is True
     assert sample_user in service_db.users
 
diff --git a/tests/app/delivery/test_send_to_providers.py b/tests/app/delivery/test_send_to_providers.py
index 9831091d1..f8dfc7863 100644
--- a/tests/app/delivery/test_send_to_providers.py
+++ b/tests/app/delivery/test_send_to_providers.py
@@ -311,7 +311,7 @@ def test_should_send_sms_sender_from_service_if_present(
 
     mmg_client.send_sms.assert_called_once_with(
         to=validate_and_format_phone_number("+447234123123"),
-        content="Dear Sir/Madam, Hello. Yours Truly, The Government.",
+        content="Sample service: Dear Sir/Madam, Hello. Yours Truly, The Government.",
         reference=str(db_notification.id),
         sender=service.sms_sender
     )
@@ -692,23 +692,26 @@ def test_should_set_international_phone_number_to_sent_status(
     assert notification.status == 'sent'
 
 
-@pytest.mark.parametrize('sms_sender, expected_sender, expected_content', [
-    ('foo', 'foo', 'bar'),
+@pytest.mark.parametrize('sms_sender, expected_sender, prefix_sms, expected_content', [
+    ('foo', 'foo', False, 'bar'),
+    ('foo', 'foo', True, 'Sample service: bar'),
     # if 40604 is actually in DB then treat that as if entered manually
-    ('40604', '40604', 'bar'),
+    ('40604', '40604', False, 'bar'),
     # 'testing' is the FROM_NUMBER during unit tests
-    ('testing', 'testing', 'Sample service: bar'),
+    ('testing', 'testing', True, 'Sample service: bar'),
+    ('testing', 'testing', False, 'bar'),
 ])
 def test_should_handle_sms_sender_and_prefix_message(
     mocker,
     sms_sender,
+    prefix_sms,
     expected_sender,
     expected_content,
     notify_db_session
 ):
     mocker.patch('app.mmg_client.send_sms')
     mocker.patch('app.delivery.send_to_providers.create_initial_notification_statistic_tasks')
-    service = create_service(sms_sender=sms_sender)
+    service = create_service(sms_sender=sms_sender, prefix_sms=prefix_sms)
     template = create_template(service, content='bar')
     notification = create_notification(template)
 
@@ -725,7 +728,7 @@ def test_should_handle_sms_sender_and_prefix_message(
 @pytest.mark.parametrize('sms_sender, prefix_setting, expected_content', [
     ('foo', True, 'Sample service: bar'),
     ('foo', False, 'bar'),
-    ('foo', None, 'bar'),
+    ('foo', None, 'Sample service: bar'),
     # 'testing' is the default SMS sender in unit tests
     ('testing', None, 'Sample service: bar'),
     ('testing', False, 'bar'),
diff --git a/tests/app/service/test_rest.py b/tests/app/service/test_rest.py
index 292b8b2e2..59a55da66 100644
--- a/tests/app/service/test_rest.py
+++ b/tests/app/service/test_rest.py
@@ -1562,18 +1562,18 @@ def test_set_sms_sender_for_service_rejects_null(client, sample_service):
     assert result['message'] == {'sms_sender': ['Field may not be null.']}
 
 
-@pytest.mark.parametrize('default_sms_sender, should_prefix', [
-    (None, True),  # None means use default
-    ('Foo', False),
+@pytest.mark.parametrize('service_attribute, should_prefix', [
+    (True, True),
+    (False, False),
 ])
 def test_prefixing_messages_based_on_sms_sender(
     client,
     notify_db_session,
-    default_sms_sender,
+    service_attribute,
     should_prefix,
 ):
     service = create_service(
-        sms_sender=default_sms_sender or current_app.config['FROM_NUMBER']
+        prefix_sms=service_attribute
     )
     create_service_sms_sender(
         service=service,