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Yes, it was possible to send a telegraph message from Moscow or St Petersburg to Tomsk in 1875. Tomsk was connected in 1863, Irkutsk in 1864 and Omsk in or before 1866.
"Map Showing the Telegraph Lines In Operation, Under Contract, and Contemplated to Complete the Circuit of the Globe, 1869". Source: HH Lloyd & Co Publishers [Public domain], via Wikimedia Commons
If you click on the map above, you can just read that the red lines show "Lines Constructed and in Operation".
According to the Ericsson website article The triumph of the telegraph,
A Danish telegraph company combined a trans-Siberian telegraph line from St Petersburg to Vladivostock with an underwater cable to China and Japan. This long connection was completed in 1871.
As noted by Henry in his comment below, there was also a line from Moscow to Sevastopol and Odessa. This was completed in 1855, and in 1863
The MoscowβTbilisi (Georgia) telegraph line, 2000 km, crossing the Caucasus was established.
Baku (Azerbaijan) was connected in 1868 and in 1877 Russia was second only to the US in kilometres of lines.