Per Twilio Rest Docs, you should be able to set the Sms Application, Voice Application, as well as a "Friendly Name". Friendly Name was in a previous version of this library when purchasing a number, but seems to have been lost.

Mike Helmick · Mike Helmick · commit b87a34ba080e · 2011-11-02T15:41:38.000-03:00
diff --git a/twilio/rest/resources.py b/twilio/rest/resources.py
@@ -859,7 +859,8 @@ def purchase(self, phone_number=None, area_code=None, voice_url=None,
                  status_callback_url=None, status_callback_method=None,
                  sms_url=None, sms_method=None, sms_fallback_url=None,
                  sms_fallback_method=None, voice_caller_id_lookup=None,
-                 account_sid=None, application_sid=None):
+                 account_sid=None, sms_application_sid=None,
+                 voice_application_sid=None, friendly_name=None):
         """
         Attempt to purchase the specified number. The only required parameters
         are **either** phone_number or area_code
@@ -880,7 +881,9 @@ def purchase(self, phone_number=None, area_code=None, voice_url=None,
                 "StatusCallbackMethod": status_callback_method,
                 "VoiceCallerIdLookup": voice_caller_id_lookup,
                 "AccountSid": account_sid,
-                "ApplicationSid": application_sid,
+                "SmsApplicationSid": sms_application_sid,
+                "VoiceApplicationSid": voice_application_sid,
+                "FriendlyName": friendly_name,
                })
 
         if phone_number:
