I could use some feedback..

I am starting a mass txt messaging service for members and I am considering purchasing the TxtMobster script at TxtMobster.com because it has everything I need (and I cannot find anything else like it)
.. However, i'm trying to figure out with several thousand members utilizing the service from their cell phones, how much bandwidth this would consume on my server? Considering that members will be utilizing the service with lists that possibly succeed several hundred subscribers, that could be a lot of data going in and out of my server each day. They say the script also uses a flat-file database or MySql which you can switch between if necessary for optimized performance or integrating 3rd party apps. Which would be a faster database for something like this?
The purpose of this service is so members can communicate time-sensitive alerts to an unlimited list of mobile and email subscribers via mobile txt. Therefor my servers HAVE to be fast..

any feedback?

I use a system that mass SMS a lot of numbers using the API from Clickatell.
There is hardly any load on the server as it sens a HTTP request to clickatell who then send the text message.

A bit of PHP code behind the script to read the list of numbers (I use flat file lists) and thats it.

Easy as :)

Clickatell provides the better service for sending sms. It simply take care of the bulk sms. Not much load will be there.

If you need some thing free you can use kannel. which is an opensource product. But I have heard many issues with it while sending the bulk sms. It will crash frequently and will create much server load than clickatell.