calls.go
func (c *CallService) GetNextCallsInRange(start time.Time, end time.Time, nextPageURI string) CallPageIterator {
	if nextPageURI == "" {
		panic("nextpageuri is empty")
	}
	iter := NewNextPageIterator(c.client, callsPathPart)
	iter.SetNextPageURI(types.NullString{Valid: true, String: nextPageURI})
	return &callDateIterator{
		start: start,
		end:   end,
		p:     iter,
	}
}
func (c *CallService) GetNextCallsInRange(start time.Time, end time.Time, nextPageURI string) CallPageIterator {
	if nextPageURI == "" {
		panic("nextpageuri is empty")
	}
	iter := NewNextPageIterator(c.client, callsPathPart)
	iter.SetNextPageURI(types.NullString{Valid: true, String: nextPageURI})
	return &callDateIterator{
		start: start,
		end:   end,
		p:     iter,
	}
}
// GetNextCallsInRange retrieves the page at the nextPageURI and continues
// retrieving pages until any results are found in the range given by start or
// end, or we determine there are no more records to be found in that range.
//
// If CallPage is non-nil, it will have at least one result.