Is there way around "Big 3" DSL co's for 'Net?

I am under the impression that one must use the "Big 3" networks on Samui (T*T, B*B or C*T) for line in, but I'm being asked to install 3K TB worth of line, as "port is full", despite B*B having been in here for last renter, AND, pay 1 YEAR up front, AND costs...a 16-18K investment, hard to do. I'm told I can "tether" iPhone into use, but I'm afraid the already HIGH fees for SIM card from phone being used (3K TB!) will go higher...the AIS "unlimited data use" is bs...after using a bit, they say, "high speed is used up, now only low, or add more" and it adds up fast. ANY IDEAS on how to do this and still be able to keep both arms? I understand "repeater" device is an option, but must still have ADSL. Thanks much! TFG