You would think that Aluminum is better then Copper when using phone lines due to the ability for sound (vibration, frequency) to travel faster through it.
EXAMPLES of the speed of sound through materials...
Air at 40oC -355 m/s
Copper - 4600 m/s
Aluminum - 6320 m/s
Dial up SHOULD work better, faster and smoother through Aluminum. HOWEVER: Aluminum expands almost 40% more than copper when heated and cooled. This can greatly affect electrical connections. YOU MAY being having more problems during summer time then winter. GET TWO PHONE LINES and TWO DIAL UP MODEMS, double your speed. Set them to dial at same time.
Also you can make a single dial up modem faster by adjusting settings.
How to make dialup faster 921.6 kbps 2012
https://www.youtube.com/watch?v=rHWzpzFdTtU