Yes, in fact many ISDN adapters and routers include STAC Compression, which lets you achieve phenomenal speeds. Consider, if you will, that an ISDN adapter with both lines (B Channels) connected to Internet Connect provides up to 128Kbits/sec without compression. With STAC compression it''s as much as 500Kbit/sec!
WARNING: STAC Compression with ISDN can be addictive!