The only thing I noticed is that the signal is consistent again after a month of continuous interruptions, couldn't hold signal for longer then 30 sec or so.
I did have this problem with Blackberry tethered to the modem. I though the interruptions were the "feature" of the BIS tethering. I now see that their 3G network did have problems internally, when you say that Banda Ancha Claro was disconnecting as well. A year ago I used BAClarop on remote computer when our local Flash DSL went down, and it held connection even for 72 hours straight.