Unfortunately, there is no good quality two-line telephone set. Any consumer-level telephone (4 lines or less) is manufactured to be disposable. Panasonic is probably the highest level of quality, but their products are expensive and not carried by all retailers. Retailers don't like to carry expensive products. The "at&t" products are about the best that you are going to find in the two-line phone price arena through mainstream retailers.
Remember that the "at&t" name is just a licensed trademark; AT&T hardware has been gone for decades and today's "at&t" has nothing to do with the manufacture of phones. This name has nothing to do with quality; it's a matter of which off-shore manufacturer came up with enough money to buy the use of the retired (AT&T) trademark.
Also, remember that consumer-level products are priced to make it difficult to justify warranty service. They may have impressive long-term or even lifetime warranties, but the shipping/handling charges and restrictions make them cost-prohibitive to the end-user.
If you want the quality of a real phone system, you are going to need to pay for one. The "buzzing" issues that have been discussed throughout this thread are indicative of how these consumer-level products DO NOT perform.
Retailers tend to leave consumers with the misconception that phone installations are a "do it yourself" project, just like painting a bedroom. "If the plug fits, then it must work, right?" These same retailers also encourage people to run their own gas lines, replace water heaters, wire hot tubs and install new electrical services on their homes.
No offense intended, but there really isn't an easy answer to your question otherwise. Buying additional retail gadgets to isolate an inherent problem with the product is like using a Band-Aid to close a gaping wound.
