10. Xiaoming's home phone number was originally a six-digit number. The first upgrade was to add the digit 8 between the first and second digits, making it a seven-digit phone number; the second upgrade was to add the digit 2 before the first digit, making it an eight-digit phone number. Xiaoming found that the eight-digit phone number after the two upgrades is exactly 81 times the original six-digit phone number. Therefore, Xiaoming's original phone number is $\qquad$
10.282500.

Let the original six-digit telephone number be $\overline{a b c d e f}$. Then, after two upgrades, the eight-digit telephone number is $\overline{2 a 8 b c c l e f}$.
According to the problem, we have $81 \times \overline{a b c d e f}=\overline{2 a 8 b c d e f}$. Let $x=b \times 10^{1}+c \times 10^{3}+d \times 10^{2}+e \times 10+f$.
Then, $81 \times a \times 10^{5}+81 x=208 \times 10^{5}+a \times 10^{6}+x$.
Solving this, we get $x=1250(208-71 a)$.
Since $0 \leqslant x<10^{5}$, we have,
$$
\begin{array}{l}
0 \leqslant 1250(208-71 a)<10^{5} . \\
\text { Therefore, } \frac{128}{71}<a \leqslant \frac{208}{71} .
\end{array}
$$

Since $a$ is an integer, we have $a=2$. Thus,
$$
x=1250 \times(208-71 \times 2)=82500 \text {. }
$$

Therefore, the original telephone number of Xiao Ming's home is 282500.