Not necessarily, if the issue is being caused by NAT timers closing ports, or the WAN connection changing the client won't make much difference.
The advantage of using a PC/MAC based client is that you can view the SIP logs and if necessary run Wireshark to capture the low-level traffic.
Don't suppose you can clarify the router you are using? Most VoIP providers require that the SIP ALG component of the router/firewall is disabled as their services generally handle NAT translation themselves and having the ALG on does often cause issues (usually the symptom of this is the 30/32 second disconnect as the final ACK or 200 OK gets missed)...
I am NOT affiliated with ANY ISP on thinkbroadband.com, I have used various ISPs and I AM knowledgeable on the subject of broadband.
"Seek and ye shall find"