I use Truemove-H 3G for Internet access as where I live that is all that is available. On the whole I am happy with speed, reliability etc. However the one thing that does annoy me is that when I have used up the data allowance on my package I have to wait until the expiry date before I can get back to a decent speed etc. I know I can have more than one SIM card but it would be so much easier if I could cancel the package when there are many days left on it and start a new package.

Does anyone know if there is a way to do this???

Yes. I am sure you can cancel an existing plan and then subscribe to a new one. You may have to ring True and use their IVR system; *9000 I think.

Simply buy more data. You can "add-on" to an existing package 1GB @ 150 baht (160.50 inc VAT) - *900*8903#

You'll be back to normal speeds until that 1GB is used up (after which you can add-on again if necessary)