Enter in your zip code, and it tells you if an umbrella is necessary.

gather.xml

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Gather action="/twilio/finley/umbrella.php" method="GET">
        <Say>Please enter your zip code, followed by the pound sign.</Say>
    </Gather>
    <Say>We didn't receive any input. Call back another time!</Say>
</Response>

Umbrella.php

<?php
  $reader = new XMLReader();
  $reader->open('http://weather.yahooapis.com/forecastrss?p=' . $_REQUEST['Digits']);

  while ($reader->read()) {
    if($reader->name == "yweather:location"){
      $location = $reader->getAttribute("city");
    }
    if($reader->name == "yweather:condition"){
      $condition = $reader->getAttribute("text");
    }
  }
  $reader->close();

  // http://developer.yahoo.com/weather/#codes
  if($condition == "rain"
    || $condition == "hurricane"
    || $condition == "tornado"
    || $condition == "showers"
    || $condition == "thunderstorms"
    || $condition == "drizzle"
    || $condition == "hail"
    || $condition == "mixed rain and sleet"
    || $condition == "scattered showers"){
      $recommendation = "So you should bring your umbrella.";
  }
  else{
    $recommendation = "So you should leave your umbrella at home.";
  }

  header("content-type: text/xml");
  echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n";
?>

<Response>
  <Say>If you are going to be in or around <?php echo $location ?>...</Say>
  <Say>It will be <?php echo $condition ?> today...</Say>
  <Say><?php echo $recommendation ?></Say>
</Response>

Just curious: how come you're not using the code attribute of yweather:condition for determining the forecast? It seems that text is more fragile (different cases and all).

Absolutely right; once those descriptions change, this is toast.

I just threw this together as a prototype for class. We are fooling around with twilio and I wanted to see how I might use it to replicate Umbrella Today.