asterisk users - Feb 2010 - Do the Linksys Sipura series have a known problem with Asterisk?

I have a Linksys Sipura SPA2102 connected to Asterisk 1.4.27 and
sometimes it doesn't connect at all. I keep getting a busy signal when
I try to dial.

It appears to happen most often when both lines are registered.

The 2 lines on Linksys lines also use different ports. Does that mean
than it is necessary to configure the 2nd line with port=5061 in
sip.conf, or can they both use 5060?

Thanks

/vfclists