Zyxel 660/661/2602

Anyone any experience with the different Zyxel models? - I am looking at them for 2 reasons:- they use the TI-AR7 chipset, and their pre-sales response is excellent (a real lesson to the supposed big-names with their lack of responses)
However, the 660 has a single fixed aerial, but the 661 allows a single upgradeable aerial, while the 2602 which is sold as a VOIP appliance (but is effectively an adsl router with voip added) has 2 upgradeable aerials which I think may improve wifi reception by increasing them from 2dbi to 5dbi aerials.
Has anyone any experience of the 2602HW/HWL and does it have any downside compared with the popular 660 models?

I have the p2602hw, the one with twin removeable aerials, the later models are fixed and single aerials.

Originally dodgy firmware but now seems to be fixed.
Changing aerials hasnt really done anything to signal strength in my experience - I did it

VOIP is fine

As to compare with others, not a clue, never used them

Thanks - can you give any feedback as to your impressions of it both from the adsl connection point of view ie does it hold signal even on dropping snr margin, what sort of line it is on etc, and what sort of range / signal you get from the wifi side of it?

Im synced at 6meg on a 3.6km line (according to an engineer), bt says I should only get 4.5ish
snr is an issue, have had to have it raised by my isp
Average download speed at present is 550Kb/s or higher

adsl - drops if snr is too low but automatically reconnects
wifi - 70% signal at 1 floor up and across by about 10m going through a floor, brick wall, and 2/3 plasterboard walls when used with my access point with 5db antenna