Hi Zerofocus,
Am in the same predicament. Hovering between 10-13G, without streaming. Don't want to think about OOB everytime i access internet near the end of the month. No LTE coverage, unfortunately, which would be the natural upgrade.
Depending on what CDMA modem you have, you can make a plan.
If you have the old AccessTel MV type - nothing much you can do.
If you have the newer Atel type - which uses a SIM card, then you're somewhat in luck, albeit not a clean solution, but do-able.
You have two choices:
1) Buy another contract without modem, either 10G for R99 or 15G for R149. Swop the SIM when you get to 15G on your original package. Yip, Schlepp, i know, + you don't exactly know when that is, but i get my daily e-mail with usage every morning, so not to difficult to figure out when to swop. Remember to swop back to the original SIM card at the beginning of the month!
Big problem here is it is a 24 months contract.:=(
2) Buy prepaid SIM, that's R499 for 25G, i think. a Bit pricey. Same process as above. You can then top-upand even re-top-up that SIM as and when it runs out. Unfortunately no portal/email to tell how much you've used, but you'll know soon enough when it stops!
I haven't tried this, but can be done, just a PITA to swop SIM's and keeping track of data usage.