Sadly, I feel that for convenience, a GSM door opener would be a better choice. It isn't range limited (so you can trigger the door as you drive up the front driveway), it is zero cost once installed, and doesn't rely on auto-connecting. The added bonus is it would work from any phone.

My research (I was bored) led me here: http://www.gsm-secure.co.uk/GSM-Access-Control.php