Change the error message for "No VOIP allowed" to "Invalid phone number"

Our error messaging coming out of the voip verification is misleading. If you enter a phone number that's valid or voip, we get a generic error.

As reported by @omadrid:

Sidenote: I think the 'voip phones not allowed' blanket error message isn't user-friendly and is often not an accurate description of the problem.

Look at the error messages that we get back from twilio in the sms client in engine. For actual voip errors we want to return the original message. But we should return better errors than we currently ar

• Return the invalid voip error for voip numbers
• Return "invalid phone numbers" for numbers