FAQs & Troubleshooting FAQ Search Results FAX-1800C Not your product? Search by FAQ ID number Search Back to FAQs & Troubleshooting. 2 Results 1.faq00002123_028 I'm using Voice Over Internet Protocol (VoIP) and am having problems sending faxes. 2.faq00002123_010 I'm using Voice Over Internet Protocol (VoIP) and am having problems receiving faxes. FAQs & Troubleshooting