For real time, reliable two way messaging you'll either want to peer with the carriers you support (using SMPP) or use an aggregator. There are a lot of aggregator options and you'll want to shop around to get the best price.<p>Using SMPP I've seen round trip times as low as 10 seconds.<p>If you want media (pictures or video), you'll want an MM7 connection.<p>I'd link to wikipedia but I'm on a mobile phone, sorry.
You could go down the SMS/email gateway route, or use a company like Clickatell to send messages for you (though I don't have any personal experience with them). But seriously, <a href="http://www.google.com/search?&q=sms+site:news.ycombinator.com" rel="nofollow">http://www.google.com/search?&q=sms+site:news.ycombinato...</a>
getting your own dedicated short code is expensive and takes a while (~2-4 months).<p>i'm not familiar with the process, but in theory you can apply for a direct connection to EACH carrier (i think you need insane volume to even attempt this and even then approval is not probable).<p>after you get your dedicated short code, most people turn to aggregators that solve the volume problem for you (i.e. clickatell).<p>others bypass the dedicated short code route for cheaper / more immediate results with a shared short code (i.e. textmarks) -- accessible with a vanity keyword.<p>you can also try setting up your own SMS gateway w/an open-source like Kannal. add nokia phones for extra style & fun points as desired.