What is the easiest, cheapest method to convert from computer/net/email to SMS and from SMS to network? I'm looking for a cheap (free is better) service for a computer application. Would I annoy google if I used a google voice account to start with? Or are there better solutions?
Clickatell[1] is cheap and provides a number of methods to send SMS: email-to-sms, HTTP (XML, SOAP, urls), SMPP, FTP. They also support inbound/two-way messaging and shortcodes, though I assume these cost a good bit more.
I've used clickatell a lot in the past (circa 2005-2007).
I'd recommend them. Be prepared to fax them details to confirm some things.
One minor frustration with them is that they have a division between their API account and their desktop messenger. It sounds like you'll be using the API first. But you cannot then use excess credits for any personal sideline messaging using their client.
We currently use http://www.mobilemarketing.net/ on a couple of projects. Their site looks terrible, but they are fairly cheap and have 'sticky' sessions. Their support is also very responsive.
Textmarks http://www.textmarks.com/ is also good but they no longer support sticky sessions. They also have free messaging if you don't mind a "powered by textmarks" with a link back to their site at the bottom of your SMS.
We offer a number of different APIs, and we can definitely handle volume. I can't cite names due to our Privacy Policy, but we're handling some large sites' SMS capabilities through our API (more than a couple ranked top 500 by Quantcast FWIW)
If you have any questions, I can answer them for you. Or if you'd like just shoot me an email - josh@eztexting.com
Where are your destination numbers from?
For US numbers you can text for free by sending an email to a carrier specific email address (nr@something.carrier.com).
Clickatell is a good option for international SMS, although they have had some issues in the past. There are a lot of similar services.
However I've never seen much cheaper than around 7 cents (when buying in bulk) for SMS to the Netherlands.
[1] http://www.clickatell.com/