When one says just "RAM", one usually specifically means "internal dynamic memory" or DRAM.
I suppose you mean the storage flash RAM when you say you're not after "internal dynamic memory" size?
Anyway, the 7610 has 16MB DRAM of which about 8MB is available after the phone as started. The N-Gage also has 16MB, of which about 10MB is available. The difference is due to different versions of Symbian OS and Series 60 (V6.1 and 1.2 on the N-Gage vs. V7.0s and 2.0 on the 7610).
The storage flash RAM size on the 7610 (which means the C-drive) is 8MB.