I had the same problem with my time capsule, even after opening up the 2 dedicated UPD ports and assigning a static ip to the phone, the calls were still dropping after a minute or two. After talking to an @home rep i went to the store are picked their branded linksys router ($20+tax w/ a $20 mail in rebate), i've cascaded my TM off the linksys and no dropped calls nor signal ever since...loving that UMA