Two-Line-Phone Question

[chicha]

Assuming I have a two-line-phone connected to an ATA, with Line 1 for telco calls and Line 2 for VOIP calls, will the phone ring for an in-coming VOIP call if the phone is in Line 1 mode? Or is the distinction between Line 1 and Line 2 solely for out-going calls, with the phone always ringing on in-coming VOIP/telco calls no matter whether the Line 1 or Line 2 switch/button is currently depressed?
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I'm finding it hard to find an ATA with a PSTN/FXO connection , two Service Lines AND built-in router. I'll go with the Sipura 2100 (has router and two Service Lines) and a two-line phone, if 2-line-phones work the way I need them to!