Eriko Kigawa voices Ginga, Uno and Tre. The three have a dialogue in the same scene in StrikerS Sound Stage X.
Yukana voices Reinforce Zwei and Lucino. Though, it's played straight is other scenes, there is a scene in StrikerS, where they have chat, but the viewer doesn't hear any dialogue, which is a bit hilarious.
Natsuko Kuwatani voices Arf, Lutecia, Sette and Auris Gaiz, but this trope is averted.
On the other hand, Lutecia lampshades in The Movie 2nd A's audio commentary that she and Arf have really similar voices and then she tries to imitate her voice (teen and child voice), much to Zafira and Fate's surprise. It's even better, if you listen carefully, Lutecia is only close to imitate Arf's voice perfectly, but there are still subtle distinctions.
Mai Nakahara voices Teana, Vice's sister Laguna, and Lutecia's mother Megane. Averted.
Mikako Takahashi voices the young Chrono and Caro. Completely averted. But played straight with Caro and Friedrich in his baby form.
In the PSP games and accompanying drama CDs - the three Aces and their Material counterparts, obviously; and every character who meets their Dark Piece doppelgängers. The latter case includes Fate, Reinforce, Vita, Shamal, Zafira, and Chrono. Doing the math, Signum is the only character who averts this trope.
Gears of Destiny also adds Yuuno and Vivio (Kaori Mizuhashi), Lily-Strosek and Amitie (Haruka Tomatsu). Thoma and Lily also meet their Dark Piece counterparts, though they actually talk with their partners rather than with their enemies.