Hi spillins,
As pointed out by RonR, the delay is purposely added to allow OBi to decode the complete caller-ID. In the US, unfortunately, caller-id is delivered after 1st ring (while in some other countries, caller-id is delivered prior to the 1st ring which will eliminate this delay).
If you do not care about caller-id directed call routing on the PSTN Line (i.e., let it ring the phone no matter who's calling), you can simply set the RingDelay parameter (as suggested by azrobert here) to 0. Then the delay would be shortened to below 1s. Furthermore, you can also lower these 2 parameters under Physical Interface/Line Port/RingValidationTime and RingIndicationDelayTime to say 200 and 256 ms respectively. Then your resulting delay would be less than 0.5s. This is probably the best it can do. The additional delay is because the ring voltage from the phone company is not passed through to the phone; but instead is relayed to the phone by the OBi (which means OBi needs to detect the ring reliably first..)
One problem to the last trick is that caller-id cannot be shown on your phone w/ the current f/w, since OBi has not decoded it yet when it starts ringing the phone. The good news is, in the upcoming 1.2 release, we have improved our implementation by allowing the device to pipeline the caller-id signal as soon as it is decoded to the phone when it is already ringing. That way your caller-id can still be shown even if RingDelay is 0 (but you still cannot do caller-id directed call routing). So please stay tuned if you do want to try out this new feature.