On placing a call, what phone number will be shown to caller

Google Voice number will be shown in caller ID only if you will have Google Voice account with similar name as Gmail Account username.

In case of not using Google Voice, (760) 705-8888 number would be visible on caller ID of receiver. Unites states customers can upgrade to full Google Voice account and can select new number which would be visible to person receiving your call.

Calls can be received on this number only if you own a full Google Voice account and these accounts are presently supported only in United States.