A gain of 3 dBm means your signal is 2 times as strong as it was before. Therefore, -60dBm is 30 times stronger than -90dBm.
Decibels are exponential creatures. A 30 dB increase means a thousand-fold increase in signal strength.
At -90 dBm, I wouldn't be surprised if your Eris starts dropping calls.
I routinely make and receive calls at levels much lower than that. I'm showing -103 right now and calls go through just fine.
--Mark