Many sites nowadays offer some type of SMS service.  But before I get into a few that I want to mention, I wanted to clear the air about how text messaging (aka SMS) works here in the US.

Unlike the rest of the World, here in the US we have packages that you purchase, or are included with the type of plan you buy on your cell/mobile phone.  So let's say you have the package that allows 200 text messages per month.  First, for the rest of the World, you need to realize that not all plans and/or companies automatically give you MMS messages to be used the same way as your SMS ones.  In other words, those 200 messages may be just your SMS (text) ONLY messages.  MMS (multimedia) ones could be extra.  Also worth mentioning, again unlike the rest of the World, the counter applies to both incoming and outgoing messages.  Yes, that's not a typo.  To spice things even further, international messages are usually not included in said plan.  Heck, they're not even included in the unlimited SMS/MMS plans that some companies offer.

So, for us here in the US, having services that interact in a positive way with the Web and how we use it is rather a big deal.  And for those curious ones, an unlimited SMS/MMS plan can range from $10/month to $25/month extra on top of your talk-time-plan (a different topic worth discussing, but not here & now).  And again, that doesn't include international (incoming or outgoing) messages.  Those are usually an extra $0.20 cents per message (again, both ways).

Data plans, to enable internet access from your cell/mobile phone, are yet an additional monthly charge.   Having SMS services, as mentioned in this article, could potentially eliminate the need for such a data plan.

So, back to the topic at hand ...

Although there are many that offer a valuable service, only a few are worth mentioning.  These, I believe, can turn any regular ol' average phone into a very useful gadget.

1. The most useful SMS service to have readily available on your phone should IMHO be Google SMS.
   This awesome collection of tools include directions, movie times & theaters, stock quotes, business listings, weather, currency conversion, airlines/flight times, calculator, area codes and a whole lot more.  Get started by texting/SMS'ing "help" (without the quotes, of course) to 466453 (it spells GOOGLE).
   
   
2. My family and I rely on Google Calendar (GCal) heavily.  And believe me, that's an understatement.  I pretty much stopped using Outlook because of it.  Heck, because of Google Docs, I've practically stopped using Microsoft's Word, Excel and Powerpoint too.  GCal can send you text messages of event notifications you have on your GCal.  Whether it's a bill that's due, a doctor's appointment, a birthday or folks coming over on a particular day, GCal can send you SMS notifications right to your phone.  And while I may seem like a Google sales rep., I'm simply a fan.  I'm just an average user that has barely started to scratch the surface with the World of Google.  To get started, send "help" to 48368 (it spells GVent).  You should get the following (or something along these lines):
   
   • Google Calendar alerts you of upcoming/new/changed events on your calendar. For info: www.google.com/calendar. To cancel text "stop" to 48368.
   • Standard msg charges apply. Text the following commands for more info: next (next event), day (todays events), nday (tomorrows events), or text a new event to add it via quick add.
   
   Don't forget to set up your GCal to send you text messages of event notifications; but do remember that message charges may apply from your cell/mobile provider.  I strongly recommend an unlimited plan of some sort.
   
   
3. Many have given up the life of shopping at brick & mortar (B&M) stores because of the online comparison shopping experience.  Savvy online shoppers use many sites like pricegrabber.com to ensure the best deal.  Personally, I have RSS feeds set up to help with such a task.  Now, however, you can have your cake and eat it too.  Shoot an item's name, and may be a brief description, to the mega retailer Amazon at 262966 (spells AMAZON) to find out their price.  Heck, why stop there, you can even buy it right there on the spot.  This should take haggling to a whole new level.
   
   For more price-comparison services, see this article.
   
   
4. Textmarks —Wow, where do I begin.  This service is awesome.  It's like having your own dynamic distribution list for things like reminders, game scores, prayer times (Athan), schedule changes, etc.   You simply create a free account, which requires a unique keywork that you must provide, and you define how the response to that keyword will be.  So imagine my keyword being "antiinertiafootball," every time someone sends a text message to 41411 with that keyword they get back whatever pre-selected response I have put in place —the time of the game we're all meeting for.  As the manager of the distribution list, I can send an update to that time to all the subscribers either via SMS or from the web.
   
   

I'm sure there are many more, like using Jott and paying friends for lunches via PayPal.  I, however, cannot speak to those first hand.  I would love to hear YOUR first-hand experience with these and others.  Chime in.