In case anyone is wondering I got it working:

from objc_util import *
import speech
import time

AVAudioSession = ObjCClass('AVAudioSession')
audioSession = AVAudioSession.sharedInstance()

oldCategory = audioSession.category()

audioSession.setCategory_error_(ns('AVAudioSessionCategoryPlayAndRecord'), None)

speech.say('hello') #like a phone call

time.sleep(1)
audioSession.setCategory_error_(ns(oldCategory), None)

speech.say('hello again') # speaker phone