Table:
|  | 2019 | 2018 | $ CHANGE | % CHANGE |
| --- | --- | --- | --- | --- |
| External service revenues | 6,427 | 6,269 | 158 | 2.5% |
| Inter-segment service revenues | 49 | 48 | 1 | 2.1% |
| Total operating service revenues | 6,476 | 6,317 | 159 | 2.5% |
| External product revenues | 2,660 | 2,497 | 163 | 6.5% |
| Inter-segment product revenues | 6 | 4 | 2 | 50.0% |
| Total operating product revenues | 2,666 | 2,501 | 165 | 6.6% |
| Total Bell Wireless revenues | 9,142 | 8,818 | 324 | 3.7% |
Paragraphs:
BELL WIRELESS RESULTS
REVENUES
Bell Wireless operating revenues increased by 3.7% in 2019, compared to 2018, driven by greater postpaid and prepaid service revenues and higher product revenues.
Service revenues increased by 2.5% in 2019, compared to last year, driven by: • Continued growth in our postpaid and prepaid subscriber base coupled with rate increases • A greater mix of customers subscribing to higher-value monthly plans including unlimited data plans launched in June 2019 • The favourable year-over-year impact from the 2018 CRTC retroactive decision on wireless domestic wholesale roaming rates
These factors were partly offset by: • Greater sales of premium handsets and more customers subscribing to higher-value monthly plans • Lower data and voice overages driven by increased customer adoption of monthly plans with higher data allotments and richer voice plans
Product revenues increased by 6.6% in 2019, compared to last year, driven by greater sales of premium handsets and the impact of higher-value rate plans in our sales mix.
Question:
What drove the change in product revenues in 2019?