Linksys Spa 841 w/ gm5 and voipstunt problem

Any body can help this!

If I put voipstunt in LINE1, GM5 with GV number the phone will not ring, but can call out w/ voipstunt.
IF I put GM5 in LINE1, and Voipstunt in LINE2, the GV# will ring, but when call out "push" the line2 button -- it said you do not have credit with GM5 credit....
Any one know how to fix this problem? Thanks!!!