_sms_delay might make some sense, especially because there might be regional or service provider dependencies that affect delay.  I'll add a setting for it.  Twilio trial accounts are a hack used during testing so we don't have to pay twilio money; I'm kind of okay with devs needing to find it here and change it if they're actually testing sms and care about truncated messages.  AFAIK that's the only reason you'd ever want to change it, sms payload length is pretty much set in stone.