Return the network provider of a Nigerian phone number

network.go

func getNetwork(phone string) string {
	networks := make(map[string][]string)
	networks["mtn"] = []string{"0803", "0806", "0814", "0810", "0813", "0814", "0816", "0703", "0706", "0903", "0906"}
	networks["9mobile"] = []string{"0809", "0817", "0818", "0908", "0909"}
	networks["airtel"] = []string{"0802", "0808", "0812", "0708", "0701", "0902", "0901", "0907"}
	networks["glo"] = []string{"0805", "0807", "0811", "0815", "0705", "0905"}

	for k, prefixes := range networks {
		for _, p := range prefixes {
			if phone[:4] == p {
				return k
			}
		}
	}
	return "N/A"
}