I do in fact run two parallel Sipgate phone lines. One of them using a GRANDSTREAM HT802 that is left on all the time, the other line is connected via a mains timer to a CISCO SPA112 box. The reason for this arrangement is so that I save the power on one line over night, but also that line gets a reboot every 24 hours in case of problems over the night. With the two boxes, I must say I have never lost either circuit anyway - except for broadband faults. I found the GRANDSTREAM box easier to set up. But Sipgate has help pages on their site anyway, and an Email help facility. I went for the box ( ATA ) option as it allows any types of phone to be used with them.
It is best if the necessary PORT FORWARDING is carried out on your router to help with reliability. Details on the Sipgate site. If your router is old and shows the facility, DISABLE SIP ALG, then disable it............................................................